Nobody messed around here Saturday. There were no flimsy challenges or stupid moves at the front of the pack during the men’s and women’s U.S. Olympic Marathon Trials. No foolish pretenders or wimpy miles once the races got underway.

On a day of huge stakes and high nerves, it was all business in the front of both fields. Meb Keflezighi, the 2004 Olympic silver medal winner, won the title in the men’s race with a finish in 2 hours 9 minutes 8 seconds. Shalane Flanagan, the 2008 Olympic bronze medalist in the 10,000 meters, claimed the women’s title in 2:25:38.

The pair ultimately took charge in two professionally executed, respectably paced, coolly run races that rewarded the athletes that pushed hard from the start and left no doubt about who deserved tickets to this summer’s London Olympic Games.

U.S. marathon record holder Ryan Hall, who led for most of the men’s race, finished second in 2:09:30 and Abdi Abdirahman, a three-time Olympian, claimed third in 2:09:47 to secure the other two men’s Olympic slots. Desiree Davila (2:25.55), the 2011 Boston Marathon runner-up, and Kara Goucher (2:26:06), the 2007 world bronze medalist in the 5,000, earned the final two women’s slots.

Both trios ran in front over their races’ waning miles, effectively settling the issue of who would represent the United States in London well before the finish.

“Having the race unfold as it did is a very good simulator for the Olympic Games,” Hall said. “The Olympic Games marathon has changed. . . . Guys aren’t afraid to run hard.”

Flanagan’s finishing time not only represented a personal best by more than three minutes, it also was the fastest marathon finish in U.S. championship and Olympic trials history. On the men’s side, Keflezighi also set a personal best, his by five seconds, just 69 days after finishing sixth in the New York City Marathon. Never had two men gone under 2:10 in a U.S. Olympic trials marathon, let alone four.

Keflezeghi, the oldest Olympic marathon trials winner in U.S. history at 36, celebrated his victory over the last mile, grabbing a small flag from a spectator and waving it as he raced to the finish, where his 74-year-old father hoisted him onto his shoulders. Flanagan, 30, meantime, said her mind was torn between elation and agony in the homestretch.

“The last mile was a cross between savoring the moment and just being really grateful that I was almost done,” she said.

Dathan Ritzenhein, a 2004 Olympian in the 10,000, produced the most dramatic moment of the day, closing a gap that reached more than 30 seconds to claim fourth place just eight seconds out of third. When he crossed the line, he crouched down, put his head in his hands, and sobbed.

Amy Hastings, a college roommate of Davila’s at Arizona State University, finished fourth for the women in 2:27:17 after dropping out of the lead pack at around the 20-mile mark. Three-time Olympian Deena Kastor (sixth in 2:30:40) and Kenyan-born Janet Cherobon-Bawcom (fifth, 2:29:45) had fallen back earlier.

The men’s race got off to a blistering start from the opening gun. Hall immediately surged to the lead and took the men through opening miles of 4:50 and 4:51, then pressed even further with several miles in the mid 4:40s.

“I was just being me,” Hall said. “I wasn’t thinking, ‘This is the Trials, I need to be conservative.’ I just wanted to air it out . . . I get excited running fast, so that’s what I decided to do.”

The women’s race began with a slow 6:11 mile, but the slugglishness got stamped out quickly as Hastings and Davila took charge. The lead women ticked through the second mile in 5:49; the third in 5:34; and the fourth in 5:30. By mile five (5:22), a massive pack after the first mile had shrunk to nine.

Neither Flanagan nor Goucher, who did not compete in 2010 because she had a baby, appreciated the aggressive tactics and the hard, fast early miles. Goucher said she had hoped for a slow pace early; she lacked confidence that she could be competitive in a faster one. Flanagan said she, too, would have preferred some slow, easy miles at the start.

Davila, however, had something else in mind.

“I thought the slower it is, the longer Kara and Amy and everyone else are going to be in it,” Davila said. “I figured, ‘Let’s get this thing going.’ ”

Goucher and Flanagan said they benefited from their new relationship as training partners, an arrangement that came about when Goucher left Alberto Salazar after seven years to join Jerry Schumacher in Portland, Ore.

“I felt very comfortable knowing Kara was in the race,” Flanagan said. “It just made it feel like we were at home working out. It kind of had this calming effect for me.”

Abdirahman enjoyed himself so much he waved his arms to try to generate noise from the crowd at around mile 18; he might have paid for that expression of enthusiasm as he fell back over the last 1.5 miles — but not enough to endanger his Olympic slot.

Keflezighi, who took three weeks off at last fall’s New York City Marathon because of bad blistering of one of his feet after accidentally leaving a breathing strip in his shoe during the race, looked fresh and ready to race Saturday.

“With about five miles to go, we were together and Meb said, ‘Hey, let’s work together to make this team,’ ” Abdirahman said. “And that’s what we did.”