NEW YORK >> Shalane Flanagan began her marathon career with a bang in New York, and the American runner figures she should end it the same way. Just one thing to do first: beat Mary Keitany.

Talk about a tough finish.

Flanagan plans to give Keitany everything she has Sunday while more than 50,000 racers from 125 countries dash through the five boroughs in the New York City Marathon. Among them is Meb Keflezighi — an American making the final 26.2-mile run of his decorated career — and Ghirmay Ghebreslassie, who last year became the youngest men’s winner at 20.

For Flanagan, though, Sunday is all about catching Keitany.

“If I need to break a leg in the race to win, I will just do anything I possibly can to put myself in position,” Flanagan said.

Beating Keitany in New York may be running’s toughest test right now. The 35-year-old Kenyan has won here three straight years, including by 3 minutes, 34 seconds last year — the biggest margin in the women’s race since 1980. Keitany has improved this year, too, setting a women’s-only marathon record of 2:17:01 in the London Marathon in April. She would be the second woman to win New York four straight years.

“In my mind, she’s the alpha racer,” Flanagan said.

The 36-year-old Flanagan finished second in New York in 2010, her marathon debut, and also won a bronze medal at the 2008 Olympics in the 10,000 meters — she was later upgraded to silver. She’s done other marathons since 2010 — including a sixth-place finish at the Rio Games in 2016 — but this is her first time running New York since that memorable first run.

Flanagan is the U.S. runner most likely to push Keitany, even after fracturing her lower back in early 2017. The injury kept Flanagan out of her hometown Boston Marathon but put her on track to push hard for a victory in New York. She’s never run more miles leading up to a marathon than for Sunday.

Inspired by the fanfare around 42-year-old Keflezighi for his final race, Flanagan is contemplating retiring if she gets her first major marathon victory.

“I just want that one last really proud feeling for myself,” she said.

Because Keitany is almost wickedly unpredictable — she burst through miles 17 and 18 in 5:08 each last year as she pulled away — Flanagan is ready to get “reckless” in her pursuit.

“I may suffer dearly,” Flanagan said, “but I’m just hoping that we all suffer because of what she does.”

Here’s what else to look for in the 41st New York City Marathon:

EYE ON SECURITY

The marathon will be held five days after the bike-path terror attack in lower Manhattan that killed eight people, putting security on the minds of planners, racers and onlookers.

Police are promising an unprecedented effort to secure the course. The security detail will include hundreds of extra uniformed patrol and plainclothes officers, roving teams of counterterrorism commandos armed with heavy weapons, bomb-sniffing dogs and rooftop snipers poised to shoot if a threat emerges.

The thought of a marathon attack hits home for Flanagan, a Massachusetts native who finished the 2013 Boston Marathon shortly before a bomb near the finish line killed three and wounded more than 260 others.

“I don’t know that there are tougher people than New Yorkers, and marathoners are pretty tough people, too,” Flanagan said. “So I think it’s an opportunity to show resilience and strength.”

HERE COMES KIPSANG

Wilson Kipsang was a late entry in the men’s field after dropping out of the Berlin Marathon after 18 ½ miles (30 kilometers) in September. The Kenyan runner was on a record pace before being halted by muscle cramping in cold, wet weather.

Kipsang is one of five men in the New York field to have run a marathon in under 2:07 — the others are Tadesse Abraham (Switzerland), Lemi Berhanu (Ethiopia), Lelisa Desisa (Ethiopia) and Geoffrey Kamworor (Kenya). There’s also Ghebreslassie, the reigning champ and first-ever major marathon winner from Eritrea. That group figures to push the pace in a fast men’s race — even with rain in the forecast.

Kipsang won New York in 2014 and finished fourth in 2015. His personal best of 2:03:13 is tops in Sunday’s field.

“Compared to 2014, I think I’m a bit stronger this time,” he said.

HART OF A CHAMPION

Comedian Kevin Hart is the biggest celebrity running New York. The diminutive fitness nut has organized a number of pop-up 5k races for fans in conjunction with his standup tours, but this will be his first marathon.

“I got little legs, but a big heart,” he said in his marathon announcement .

Some other notable runners: former New York Giants running back Tiki Barber, celebrity chef Richard Blais and model Karlie Kloss.