By Gene Cherry

EUGENE, Oregon (Reuters) - World indoor champion Boris Berian was upset in the men's 800 meters, while Alysia Montano and Brenda Martinez had their Rio hopes dashed when they became entangled in the women's race at the American Olympic trials on Monday.

Collegiate champion Clayton Murphy surged past Berian to punch his Rio ticket in 1:44.76, 16 hundredths of a second faster than Berian who still made the team for Brazil along with Charles Jock.

The biggest drama came in the women's race over two laps, however, with little-known Kate Grace winning in 1:59.10 after Montano and Martinez came together before tumbling to the track on the final bend.

Without naming names, Martinez insisted she was clipped by a runner and Montano denied she was the guilty party.

"I don't know what happened to Brenda," the tearful Montano said. "She ended up tripping and I found myself jumping around her and someone kicked me out from behind. What can I do in that situation? I didn't touch anyone."

Martinez said she had been unable to regain her composure after the incident.

"I just tried catching my fall but by then they were already making another gear, another move," said the 2013 world bronze medalist, who finished seventh in 2:06.63.

A distraught Montano, who believes doping Russian athletes cheated her out of a medal at the 2012 Olympics, lay on the track before getting up, jogging a bit, then falling to her knees before eventually reaching the line in 3:06.77.

Officials ruled the contact incidental and said there would be no disqualification.

World indoor silver medallist Ajee Wilson claimed second in 1:59.51 with Chrishuna Williams taking third.

Men's winner Murphy said he was not sure he could catch Berian after the indoor champion had sprinted to the lead after a hectic 350 metres.

"But when I came off the top of the curve in second I had confidence that I could be in top three," said the 21-year-old.

Berian, who two years ago was flipping hamburgers for a living, was philosophical about a defeat which still saw him clinch his place on the Olympic team.

"It’s all worth it and I’m just so proud right now," the 23-year-old said.

Olympic 10,000 metres silver medallist Galen Rupp, already on the American team in the marathon and 10,000, squeezed into Saturday's 5,000 metres final as the 12th qualifier, clocking 13:49.50.

Woody Kincaid led qualifying (13:47.86) with the better known Ryan Hill and Bernard Lagat also advancing.

The U.S. pole vault team for Rio will all be first time Olympians. World indoor silver medallist Sam Kendricks led the way with 5.91 metres for the win, while Cale Simmons (5.65m) and Logan Cunningham (5.60m) took the next two spots.

The trials, at the University of Oregon's Hayward Field, take a day off on Tuesday before resuming on Wednesday. Only the top three finishers in each event qualify for Rio.

(Editing by Nick Mulvenney)