This race was over as soon as John Korir stopped looking over his shoulder and started glancing at his watch.
Once he broke away from the pack midway along the Newton hills there was little question that the 28-year-old Kenyan would win the 129th Boston Marathon on Monday morning by a comfortable margin, which turned out to be 19 seconds over Tanzania’s Alphonce Felix Simbu.
The only question was how fast the Chicago champion could motor on the Brookline flats with nobody to push him. The answer was a blistering 2 hours, 4 minutes, 45 seconds, the third-fastest time in race history and second-fastest by a victor.
Not since countryman Geoffrey Mutai posted a world-best 2:03:02 ahead of a howling headwind in 2011 with Moses Mosop four seconds back had anyone gone that fast on this lumpy layout.
And not that the family was keeping track, but Korir’s clocking was nearly eight minutes quicker than brother Wesley’s time when he won here amid sapping heat in 2012.
This was the first time that siblings have worn the laurel wreath at this holiday jaunt and Wesley, who’d offered his kid brother (by 14 years) sage course advice, was on hand to see him master it. “He said, you believe in yourself and you can make it,” said John, who was fourth here last year.
Making it meant getting to the Boylston Street finish line standing up. And 100 yards after the start it was far from certain that Korir would get there when he tumbled after being tripped from behind.
“What came to my mind was, should I stay down or should I wake up and go?” said Korir, who stuffed his dislodged bib into his shorts. “So something told me to wake up and go and that everything will be OK.”
Had Korir not regained his feet quickly his rivals would have left him behind. With Ethiopian defending champion Sisay Lemma leading the way the pack was under course-record pace through the midway point.
At the firehouse turn heading into the hills more than a dozen men still were within a couple of strides of one another including two-time titlist Evans Chebet and US Olympians Conner Mantz and Clayton Young.
As far as Korir was concerned that was a dozen too many. So the Bibless Wonder busted a move on the way to Heartbreak Hill and quickly was all by himself.
“That was the plan,” said Korir, whose 2:02:44 in Chicago was surpassed there only by Kelvin Kiptum’s world-record 2:00:35. “We said at 20 miles I will try and make the move … I was going to make a big gap. And if anyone tries to close he will not be able to close.”
In just a mile Korir increased his lead to 18 seconds. By the time he neared Cleveland Circle and the final 4 miles his pursuers had been reduced to four.
Lemma, bidding to be the first Ethiopian champion to repeat, had blown up in Wellesley and dropped out. Chebet, who’d won here in 2022 and 2023, was well in the rearview mirror.
By Coolidge Corner Korir’s lead was more than 40 seconds and the race was for second among Simbu, Mantz, and Kenya’s CyBrian Kotut.
Kotut, who was ninth last year, was toughened by the experience and went on to finish second in Berlin last autumn. “I am a different, stronger athlete mentally, courtesy of Boston,” he said.
Simbu hadn’t run here before but had received a thorough briefing from countryman Gabriel Geay, who was runner-up two years ago. “After talking to him I started to prepare for this race by going up hills,” Simbu said.
Mantz had run here two years ago, unwisely overestimated his chances, and finished 11th. But after coming eighth in the Olympics and sixth in New York he had the confidence to stay with the leaders regardless of the pace.
So coming out of Kenmore Square there were three men going hard for two podium spots over the final mile. Mantz looked good for one of them until Simbu and Kotut outsprinted him down the stretch.
“A little bit tough to swallow,” said Mantz, who ended up four seconds behind Kotut in fourth. “The goal was to prove that I could be in a position to win and that was being on the podium. Missing it and getting outkicked for the last 300 meters was a little bitter but it was probably the best race I’ve had, so I’m very happy about that.”
Mantz’s time of 2:05:08 was the fastest by an American here since Ryan Hall posted a 2:04:58 when he placed fourth in 2011. And Korir’s was the fastest by a victor who wasn’t airlifted from behind.
His triumph, the fifth by a Kenyan in the last six races here, was an occasion for sibling revelry. Wesley, who began jumping for joy when he spotted John sprinting toward the tape, embraced his new peer.
“Today I have made it,” the new champion said. “And we are happy as the Korir family to be two brothers winning Boston.”
John Powers can be reached at john.powers@globe.com.