Nick Willis knew he had a chance with one lap, or 200 meters, remaining in the Wanamaker Mile at the Millrose Games in New York City on Saturday afternoon. He saw that his split time was within range of his goal, if only he could find that gear for his finishing kick. But that gear, the familiar one that had helped drive him to two Olympic medals in the men’s 1,500 meters during his decorated career?

“It wasn’t actually there,” Willis said. “I felt like I wasn’t tying up, but I wasn’t accelerating either, so I knew it was going to be close.”

A five-time Olympian for New Zealand and the oldest athlete in the field, Willis, 38, stuck to the back of Hobbs Kessler, his 18-year-old training partner, before they charged through the finish line. As Willis doubled over with his hands on his knees, the public-address announcer at the Armory Track and Field Center in Upper Manhattan soon broadcast his time — 3 minutes 59.71 seconds — which set off one of the more remarkable celebrations for a ninth-place finish in the history of the Millrose Games.

Cheers from the crowd. Hugs from his fellow athletes. And a victory lap to commemorate breaking four minutes in the mile for the 20th straight year, which extended his own record.

“It’s outrageous,” said Geordie Beamish, who won the men’s 3,000 meters on Saturday. “One sub-four is pretty bloody good. Twenty years in a row? That’s something else.”

There is a tendency in sports to celebrate the next best thing, the prodigies who burst onto the scene. But January has been quite a month for runners of a different vintage. A couple of weeks ago, Sara Hall, 38, set an American record for the women’s half-marathon, while Keira D’Amato, 37, broke the longstanding American record for the women’s marathon, both in Houston.

“Two mothers in their late 30s just changed the history books in the same day,” D’Amato said after her run.

Like Hall and D’Amato, Willis has not been immune to setbacks and injury. Among other procedures, he had hip surgery in 2009 and knee surgery in 2010. He recently told GQ magazine that he had also had “five or six stress fractures” since his streak began, setbacks that sidelined him for months at a time. But he still found the resolve to squeeze in at least one sub-four mile in each of those years — and 63 of them overall, according to Citius Mag, the track and field website.

On Saturday, Willis thought back to his first big splash on the international scene — a gold medal in the 1,500 meters at the 2006 Commonwealth Games. He was just 22 at the time, and he liked the idea that he could help inspire a generation of young runners in New Zealand. It was something that motivated him for a number of years.

But at some point along his journey as a professional runner, his fan base changed. The Kiwi kids stopped idolizing him, he said, as he slowly morphed into a poster boy for weekend warriors. He began hearing from a lot of former athletes.

“Life got in the way and they got out of shape,” Willis said, “and they say, ‘Man, you’re doing this to represent us, and it’s motivated me to buy a pair of shoes and get out there again.’ So it’s gone full circle.”

This is an obvious but necessary observation: Breaking four minutes for the mile is extraordinarily difficult. No human in history achieved the feat until May 6, 1954, when Roger Bannister, a British medical student, ran the distance in 3:59.4 on a cinder track in Oxford, England. The sub-four mile has retained its allure through the decades, a sort of demarcation line of world-class fitness for male middle-distance runners.

It has certainly not gotten any easier for Willis, whose race on Saturday was his second crack at a sub-four mile since the start of the year. Accompanied by a couple of teammates and a documentary film crew, he raced on the Armory track just after midnight on New Year’s Day with the hope of getting it out of the way early, before fate, age or injury could intervene. But in an empty building, he finished in 4:00.22.

On Saturday, Willis was back, and he said he had a lot of fun — for much of the afternoon, at least. He enjoyed his warm-up with Kessler. He enjoyed hearing his name during introductions and jogging onto the track between two rows of oversize sparklers. He enjoyed approaching the start line. And he even enjoyed running the first couple of laps. And then? “It wasn’t fun,” he said.

The mile is a punishing test of speed and endurance, and Willis found himself wondering, as he often does these days:

“Sometimes that question creeps into your mind,” he said. “It’s not the same as training, because with training you get breaks to recalibrate and be like, ‘OK, I can cope with this pain.’”

Willis has nothing left to prove. He has a storied professional running career, a family and a full-time job working for Tracksmith, a running apparel company. Yet, he keeps returning. He values the camaraderie of training in Ann Arbor, Mich., alongside Kessler and Mason Ferlic, an Olympic steeplechaser, while continuing to work with his longtime coach, Ron Warhurst.

“It’s such a fun social outlet for me,” Willis said, “and I enjoy keeping the young kids honest whenever I can.”

He also loves to compete, and the streak, in its own way, has helped him reshape his ambitions. He may not vie for wins anymore. It was not lost on him, for example, that he finished nearly nine seconds behind the winner, Ollie Hoare.

“But having a sub-four is still that carrot to chase a worthy goal,” Willis said, adding: “I’m very proud of it.”

He was cagey about his future, though he did say he would never “retire” from running. He has pared back his weekly mileage, and he plans to do just four or five workouts a week moving forward, most of them with his teammates.

As for racing, Willis offered nothing definitive. But age has emerged as a worthy adversary in recent years, and Willis has a nice win streak going.