BOSTON -- Sisay Lemma scorched the first half of the Boston Marathon course Monday, setting a record pace to build a lead of more than half a mile.

Then the weather heated up, and the 34-year-old Ethiopian slowed down.

After running alone for most of the morning, Lemma held on down Boylston Street to finish in 2 hours, 6 minutes, 17 seconds -- the 10th-fastest time in the race's 128-year history.

"I decided that I wanted to start fast early," said Lemma, who dropped to the pavement and rolled onto his back, smiling, after crossing the finish line. "I kept the pace and I won."

Lemma, the 2021 London champion, arrived in Boston with the fastest time in the field -- just the fourth person ever to break 2:02:00 when he won in Valencia last year. And he showed it on the course Monday, separating himself from the pack in Ashland and opening a lead of more than half a mile.

Lemma ran the first half in 1:00:19 -- 99 seconds faster than Geoffrey Mutai's course record pace in 2011, when he finished in 2:03:02 -- the fastest marathon in history to that point. Fellow Ethiopian Mohamed Esa closed the gap through the last few miles, finishing second by 41 seconds; two-time defending champion Evans Chebet was third.

Hopkinton celebrated its 100th anniversary as the starting line for the world's oldest and most prestigious marathon, sending off a field of 17 former champions and nearly 30,000 other runners. Near the finish on Boylston Street 26.2 miles away, officials observed the anniversary of the 2013 bombing that killed three and wounded hundreds more.

Sunny skies and minimal wind greeted the runners, with temperatures that rose into the 60s in late morning. As the field went through Natick, the fourth of eight cities and towns on the route, athletes splashed water on themselves to cool off.

"We couldn't ask for a better day," former New England Patriots tight end Rob Gronkowski, the grand marshal, said before climbing into an electric car that would carry him along the course. "The city of Boston always comes out to support, no matter the event. The weather is perfection, the energy is popping."

The festivities began around 6 a.m., when race director Dave McGillivray sent off about 30 Massachusetts National Guard members. Lt. Col. Paula Reichert Karsten, one of the marchers, said she wanted to be part of a "quintessential Massachusetts event."

The start line was painted to say "100 years in Hopkinton," commemorating the 1924 move from Ashland to Hopkinton to conform to the official Olympic Marathon distance. The announcer welcomed the gathering crowds to the "sleepy little town of Hopkinton, 364 days of the year."

"In Hopkinton, it's probably the coolest thing about the town," said Maggie Agosto, a 16-year-old resident who went to the start line with a friend to watch the race.

The annual race on Patriots' Day, the state holiday that commemorates the start of the Revolutionary War, also fell on One Boston Day, when the city remembers the victims of the marathon bombings. At the finish line on Boylston Street, bagpipes accompanied Gov. Maura Healey, Boston Mayor Michelle Wu and family members of the victims as they laid a pair of wreaths at the sites of the explosions.

Information from The Associated Press was used in this report.