TEMPE, Ariz. - Haile Gebrselassie shattered the world half marathon record by 21 seconds Sunday while running the last half of the Rock 'N' Roll Arizona marathon.

He also broke the 20-kilometer world mark en route. It marked the 19th and 20th times the diminutive Ethiopian has broken world records in his career.

"This one is so fantastic because this is my first one in America," he said. "It's a little special to me. It's really, really wonderful."

His half marathon time of 58 minutes, 55 seconds on a clear, crisp morning through the streets of Phoenix, Scottsdale and Tempe broke the mark of 59:16 set by 18-year-old Kenyan Samuel Wanjiru in Rotterdam, The Netherlands, last Sept. 11.

His 20-kilometer time, also officially clocked, was 55:48. That broke the world record held by his longtime rival, Paul Tergat of Kenya, of 56:18 set in the Stramilano, Italy, half marathon on April 4, 1998.

While nearly 34,000 took part in the marathon and related running events on Sunday, only Gebrselassie and four pacesetters took off from the midpoint of the marathon course. Initially, he was slower than Wanjiru's world-record pace, but that changed when the 32-year-old four-time world champion and two-time Olympic gold medalist took off on his own some 10 kilometers into his race.

That was by design, he said.

"That was our plan. We didn't expect the first part of the race to be fast," Gebrselassie said. "Our plan was for the second part. My plan was to run under 59 minutes and that is what we did."

With rock bands playing each mile along the way, Gebrselassie showed no signs of laboring, looking as if he was on a simple morning run. He averaged less than 4 1/2 minutes per mile over the 13.1 miles.

Gebrselassie won the Olympic gold medal at 10,000 meters in 1996 and 2000 but has not run on the track since his fifth-place finish at the 2004 Athens Games. Instead, he switched to the roads, where he hopes to add a gold medal in the marathon at the 2008 Olympics in Beijing.

Last October, he aimed for Tergat's world marathon record of 2 hours, 4 minutes, 55 seconds at the Rotterdam Marathon but came up short at 2:06.20.

He has been training at 9,800 feet near his home in Ethiopia.

Sunday's time sends a message to Gebrselassie's foes that he is in top shape for the April 23 London Marathon, where Tergat will be among the competitors.

"You can see from today's record," he said when asked about his condition for London. "I hope I will do very good in the London Marathon."

There will be no "rabbits" setting the pace in that one, so Gebrselassie downplayed the opportunity for a world record there.

"London is going to be something different because everybody wants to run to win," he said. "I'm OK if I win. If I do not break the world record but win in London, it is something special. But we'll see. Anything is possible."

Cheering fans waved Ethiopian flags as he neared the finish line on the Arizona State University campus. When he crossed the finish line, a few fans and friends surrounded him, chanting "Haile! Ethiopia!" He blew kisses to the crowd.

"Everywhere in the world, there are Ethiopians," he said.