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Meb Keflezighi has become the first American male to win the Boston Marathon since 1983 – one year after bombings left three dead and 264 injured.

Kenya’s Rita Jeptoo also successfully defended her women’s title, becoming the 7th 3-time winner of the race.

Keflezighi crossed the finish line with a time of 2:08:37, 11 seconds ahead of second place finisher Wilson Chebet of Kenya.

The 38-year-old from San Diego looked over his shoulder several times over the final mile. After realizing he wouldn't be caught, he raised his sunglasses, began pumping his right fist and made the sign of the cross

Keflezighi is a three-time Olympian who won the 2009 New York City Marathon and a silver medal at the 2004 Olympics in Athens. His previous best finish at the Boston Marathon was third in 2006.

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The last American to win the Boston Marathon was Greg Meyer, who recorded a time of 2:09:00 in 1983.

Keflezighi ran the race wearing an official runner's bib with the names of the three people killed in last year's marathon as well as the name of a police officer from MIT who was allegedly killed by the bombing suspect several days later. The victims were 8-year-old Martin Richard, 29-year-old Krystle Campbell and 23-year-old Lu Lingzi. MIT Officer Sean Collier was shot three days after the marathon.

Keflezighi said he hoped to have his picture taken with the victims' families after his win Monday, but they weren't immediately available.

Jeptoo won the women’s edition of the race in a course-record time of 2:18:57. Margaret Okayo of Kenya, the previous record holder, finished with a time of 2:20:43 in 2002.

Last year, Jeptoo said it was “very difficult to be happy” with her win because of the attacks.

"If I'm going to win again, I hope I can be happier and to show people, like I was supposed to last year,” Jeptoo said prior to the start of Monday’s race.

On Twitter, President Barack Obama congratulated Keflizighi and Shalane Flanagan, the top American finisher among the women, "for making American proud!"

"All of today's runners showed the world the meaning of #BostonStrong," Obama wrote.

White House spokesman Jay Carney said Keflezighi's becoming the first American man to win the marathon in 31 years was "quite an accomplishment and a great year to do it."

Runners were expected to remain on the course for several hours after the winners crossed the finish line. Last year, the bombs went off at 2:49 p.m., as spectators crowded around the finish the line to cheer the still-arriving runners about five hours into the race.

Dzhokhar Tsarnaev, 20, is awaiting trial in the attack and could get the death penalty. Prosecutors said he and his older brother — ethnic Chechens who came to the U.S. from Russia more than a decade ago — carried out the attack in retaliation for U.S. wars in Muslim lands.

Tamerlan Tsarnaev, 26, died in a shootout with police days after the bombings.

Security was noticeably heightened Monday as runners kicked off the annual race. Helicopters could be seen circling overhead as well as bomb-sniffing dogs checking through trash cans. State and local police were also spotted on the rooftops of some buildings.

Massachusetts Gov. Deval Patrick set off the first entrants in the mobility impaired division, who crossed the starting line at 8:50 a.m.

Despite the increased security, the mood was festive at the finish line. Spontaneous applause broke out as a group of Boston police officers walked near the site of last year's twin bombing. Children danced as the Rolling Stones' song "Start Me Up" blared over the loudspeakers. Runners were dropped off by buses bearing the message, "Boston Strong."

"There'll be considerably more police presence," Patrick said on CBS' "Face the Nation". "But we also don't want to have it, you know, kind of a race through a militarized zone. So it's about striking a balance, and I think we have struck that balance."

On Monday, spectators were forced to go through tight security checkpoints before being allowed near Hopkinton Common for the start of the race. A moment of silence was observed before the marathon got under way.

A woman in Hopkinton who watches the start of the marathon in most years says she's never seen anything close to this level of security. But Jean Bertschman says everyone has been "very pleasant."

The wheelchair division began at 9:17, followed by the handcycles at 9:22 and the elite women at 9:32. The elite men and the first wave of amateur runners kicked off at 10. There are four waves in total, the last started at 11:25.

Joe Ebert, 61, of Hampton, N.H., was cheering on his son-in-law near the spot in downtown Boston where the bombs went off. He was in the same area last year at the time of the attack.

"I wanted to be in this spot," said Ebert, who wore a jacket and medal from when he ran the race in 2010. "Just wanted to let them know that they can't beat us down. I think it makes us all stronger when something like that happens."

Sabrina Dello Russo, 38, of South Boston, was running her first marathon for a good friend, Roseann Sdoia, who lost her right leg in the bombing.

"She is my inspiration from day one last year when I saw her in the ICU. Every run I do, she is in the back of my head, and she will be keeping me going today," Dello Russo said.

Approximately 36,000 runners registered for the 118th running of the race, the oldest annual marathon in the world. That's approximately 9,000 more than last year's field, with many of them coming to show support for the event and the city that was shocked by the attack on its signature sporting event. Race organizers expanded the field to make room for approximately 5,000 runners who were on the course when the explosions shook Boylston Street in the heart of Boston's Back Bay on the afternoon of last April 15.

More than 3,500 police officers -- double the usual number -- were out along the 26.2-mile course, including undercover officers with special training. At least 100 strategically positioned video cameras will monitor the crowds.

The expanded security effort required state and local officials to move their regular "tabletop exercise" to study the course and plan for possible emergencies from the state's emergency bunker in Framingham to the a convention center in the city. The crowd grew from what usually is about 100 to more than 450, according to Boston Athletic Association executive director Tom Grilk, who is in charge of organizing the race.

Patrick said there have been no specific threats against the race, which is held on Patriots' Day, a state holiday in Massachusetts and Maine that commemorates the Revolutionary War battles of Lexington and Concord. In addition to the marathon, the day also features the Boston Red Sox hosting the only scheduled morning Major League Baseball game.

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The Associated Press contributed to this report.