The 36-year-old Ukrainian, who holds the IBF, IBO, WBO and WBA crowns, was never seriously troubled by the 32-year-old who saw his unbeaten record snap after 27 wins in 27 fights.

His older brother Vitali Klitschko holds the WBC crown.

"It was a very tough fight and Mariusz had to take a lot of punches," Klitschko said in a ringside interview. "I thought that Wach would go down but he fought on."

Klitschko also remembered late coach Emanuel Steward who died on October 25.

"On July 7 after our last fight we sang happy birthday to him. We miss you, we love you, you are always here in the ring, thank you Emanuel," said Klitschko.

With Hollywood actor Sylvester Stallone, who is co-producing 'Rocky - the Musical' with the Klitschko brothers, making a pre-fight appearance in the ring for the 16,000 fans in the O2 arena, Klitschko set the pace from the first round.

Wach may be the first opponent taller than Klitschko, who is 1.98 metres, but he lacked the speed of the Ukrainian.

The Pole did get one chance in the fifth round, pummelling his opponent after a huge right to the head but the Ukrainian was saved by the bell.

It was back to form in the following rounds and Klitschko, who improved his record to 59 wins from 62 fights, pinned Wach to the ropes in the seventh and eighth but failed to knock him down.

Instead Klitschko dished out painful punishment in the final rounds with the eyes of fans on referee Eddie Cotton to see whether he would put an end to it.

The three judges gave Klitschko a 120-107 120-107 119-109 victory.

Del Potro, fresh from beating the Swiss in the Basel final a fortnight ago, claimed a 7-6 4-6 6-3 victory at the O2 Arena to guarantee himself runner-up spot in Group B with a 2-1 record, the same as defending champion Federer who will meet Andy Murray for third time in London this year in the other semi-final.

Federer won his seventh Wimbledon title this year when he beat Murray in the final but a few weeks later the Briton gained revenge in the Olympic gold medal match.

The Swiss 31-year-old, winner of 12 consecutive matches at the tournament since a semi-final defeat by Nikolay Davydenko in 2009, had already qualified for the semis before walking on court to face del Potro and produced a patchy display.

David Ferrer beat Janko Tipsarevic 4-6 6-3 6-1 in the last round-robin match in the evening to also end with two wins and one defeat but the Spaniard missed out on sets countback.

The final day of group play began with seven scenarios still possible in Group B.

Del Potro's three-set win ended Ferrer's semi-final hopes but muddied the waters as far Sunday's schedule was concerned because the outcome of the Ferrer v Tipsarevic clash would bizarrely decide whether Federer or del Potro won the group.

Victory for Tipsarevic would have seen Del Potro top the group because of a better head-to-head record against Federer but Ferrer's victory and a three-way tie meant Federer 5-2 sets tally earned him the group winners' spot.

Del Potro ended 5-3 with Ferrer 4-4.

Spain's Ferrer had been relying on a Federer victory to keep his hopes of a semi-final place alive.

"I was actually thinking more about David than I was thinking about whether I play Andy (Murray) or Novak (Djokovic), to be honest," Federer, who will contest a 10th semi-final in 11 appearances at the tournament, told reporters.

"I really wanted to give him a chance and give myself the best possible preparation for the semis.

"I really hoped I could win. I'm more disappointed for him than about losing today, to be quite honest."

BIG GUY

Del Potro's defeat of Federer was reminiscent of 2009 when he also beat the Swiss in the final round of group play before going on to reach the final.

"Now you have three big names in the semi-finals and one big guy," the 1.98m Del Potro told reporters after his second indoor victory over Federer in as many weeks.

Federer looked untroubled on his serve in the opening set against the 24-year-old but paid the price for failing to convert two break points that would have given him a 5-3 lead.

The 17-times grand slam champion then played an error-strewn tiebreak which Del Potro took 7-3.

Federer was immaculate in the second set, breaking to love in the opening game and dropping just five points on his own delivery as he set up a decider.

Just when it seemed a 13th consecutive victory was looming, however, Federer was broken out of the blue to trail 2-0 in the decider and Del Potro was rock solid thereafter.

"It's indoor tennis, he has a big serve and all those things. But still the surface plays somewhat slow so I expect myself to get more returns into play," Federer said of a rather toothless showing in the deciding set.

"But it's important to move on right now. Mentally, it's important to look ahead and rest because it's a quick turnaround till tomorrow."

Despite an impressive performance Del Potro played down his chances of landing his biggest title since winning the U.S. Open in 2009, also against Federer.

"I don't know who is the favorite," Del Potro, a finalist here three years ago, said. "Djokovic, Murray or Federer can win the tournament. I can tell you I'm the No. 4 for sure."

In doubles play, top seeds and three-times former champions Bob and Mike Bryan lost to India's Leander Paes and Radek Stepanek, meaning the Americans missed out on the semi-finals.

Paes and Stepanek won a match tiebreak 10-7 and will face Mahesh Bhupathi and Rohan Bopanna in the semi-finals. In the other semi-final Britain's Jonathan Marray and Dane Frederik Nielson wil play Spaniards Marcel Granollers and Marc Lopez.

(Editing by Ed Osmond)

These fears are based on misinterpretations of the . On the 21st, the date of the winter solstice, a calendar cycle called the 13th b'ak'tun comes to an end. Although Maya scholars agree that the ancient Maya would not have seen this day as apocalyptic, rumors have spread that a cosmic event may end life on Earth on that day.

Thus NASA's involvement. The space agency maintains a 2012 information page , such as the idea that a rogue planet will hit Earth on Dec. 21, killing everyone. (In fact, astronomers are quite good at detecting near-Earth objects, and any wandering planet scheduled to collide with Earth in three weeks would be the brightest object in the sky behind the sun and moon by now.)

"There is no true issue here," David Morrison, an astrobiologist at NASA Ames Research Center, said during aevent today (Nov. 28). "This is just a manufactured fantasy." []

Real-world consequences

Unfortunately, Morrison said, the fantasy has real-life consequences. As one of NASA's prominent speakers on 2012 doomsday myths, Morrison said, he receives many emails and letters from worried citizens, particularly young people. Some say they can't eat, or are too worried to sleep, Morrison said. Others say they're suicidal.

"While this is a joke to some people and a mystery to others, there is a core of people who are truly concerned," he said.

Not everythinks the world will end on Dec. 21. Some, inspired by New Age philosophies, expect a day of universal peace and spiritual transformation. But it's impressionable kids who have NASA officials worried.

"I think it's evil for people to propagate rumors on the Internet to frighten children," Morrison said.

Myths and misconceptions

NASA scientists took questions via social media in the hour-long video chat, debunking doomsday myths from theto the danger of killer solar flares.

In fact, said NASA heliophysicist Lika Guhathakurta, it's true that the sun is currently in an active phase of its cycle, meaning electromagnetic energy has picked up. Large solar flares can impact electronics and navigation systems on Earth, but satellites monitoring the sun give plenty of warning and allow officials to compensate for the extra electromagnetic activity when it hits our atmosphere. What's more, Guhathakurta said, this particularis the "wimpiest" in some time scientists have no reason to expect solar storms beyond what our planet has weathered in the past.

Nor are any near-Earth objects, planetary or otherwise, threatening to slam into our planet on Dec. 21, said Don Yeomans, a planetary scientist who tracks near-Earth objects at NASA's Jet Propulsion Laboratory. The only close asteroid approach on the horizon is forecast to occur on Feb. 13, 2013, when an asteroid will pass within 4.5 Earth radii to our planet (for perspective, Earth's radius is 3,963 miles, or 6,378 kilometers). The asteroid is not going to hit Earth, Yeomans said.

Other rumors that the Earth's magnetic field will suddenly reverse or that the planet will travel almost 30,000 light-years and fall into the black hole at the center of the Milky Way galaxy were also dismissed. (A light-year is the distance light travels in one year, or about 6 trillion miles, or 10 trillion km.)

One popular rumor that the planet will undergo a complete blackout from Dec. 23 to 25 earned a "What?" and blank looks from the panel of scientists.

Ultimately, concerns about Earth's fate would be better focused on slow-acting problems such asrather than some sort of cosmic catastrophe, said Andrew Fraknoi, an astronomer at Foothill College in California.

Mitzi Adams, a heliophysicist at NASA's Marshall Space Flight Center, agreed.

"The greatest threat to Earth in 2012, at the end of this year and in the future, is just from the human race itself," Adams said.

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