For Neynens, the 2013 London Marathon and 2013 Boston Marathon always will be linked. A week ago, Neynens, who lives in Enfield, Nova Scotia, waited on Boylston Street for his wife, Colleen, to finish Boston. Colleen spotted Harry in the crowd at the 26-mile mark, ran over, and kissed her husband. Then Harry walked down Boylston Street to catch up with Colleen once she crossed the line. She finished as 4 hours 7 minutes 12 seconds flashed on the race clock. He found himself 100 yards away from the bomb explosions and he saw some of the critically injured victims.

“I had a hard day out here,” said Neynens, who wore a 2013 Boston Marathon hat during his London run and finished in 2:48:09. “I was hurting, but obviously I was not hurting near as much as the injuries that I saw, people who lost their legs. I finished for all those people who were hurt and those people who couldn’t finish last Monday.

“There was a banner we passed around Mile 25 that said, ‘Run if you can. Walk if you must. But finish for Boston.’ That meant a lot to everybody. It was great to see the support of everybody out there for the runners and for Boston.”

Sunday was a perfect day for a marathon. And it stayed that way as more than 36,000 runners completed 26.2 miles.

From the Greenwich Park start to the Mall finish in front of Buckingham Palace, runners and spectators kept Boston in their thoughts. In the starting area, a pair of runners held up a red and white banner that simply read: “For Boston.” As enthusiastic, undeterred spectators awaited runners at Tower Bridge, along the River Thames and in the shadow of Big Ben, that seemed a sentiment shared throughout London.

The perfect marathon day quickly turned into a tribute to Boston’s strength and a celebration of the human spirit.

During a prerace ceremony, runners paused for 30 seconds of silence in honor of the Boston Marathon bombing victims. Many entrants bowed their heads, looking down at bib numbers and race clothes adorned with black ribbons. Some previous Boston Marathon participants wore their long-sleeved finisher’s T-shirts and commemorative race hats with the famous BAA unicorn logo, other London entrants showed solidarity with Red Sox hats. Ashley Dobson of London wore a Kevin Garnett jersey “out of respect for Boston.” Around Mile 10, a band played “Sweet Caroline.”

“It was really emotional right till the end,” said Lynda Coye of Boston, who raced with a Red Sox cap and finished in 3:39:36. “At the finish line, what happened on Monday ran through my mind. I feel so bad for that little boy who died. I can’t get it out of my head. Any time I felt like I was slowing down, I thought, ‘People died and I’m here. I need to push it as much as I can.’ It was just emotional coming over here. I didn’t want to leave the United States. But then, I thought, ‘Life goes on.’ ”

That message came through, too, as the massive field raced under sunny skies with early temperatures in the mid-40s, ideal weather identical to what runners enjoyed in Hopkinton almost a week ago. The sunny day seemed to encourage larger-than-usual crowds along the course, according to several runners who previously participated in the London Marathon. Estimates put the crowd at 700,000.

Given the large numbers, spectators appeared undaunted by the Boston terrorist attack and determined to experience the whole marathon spectacle. They cheered the efforts of everyone from men’s champion Tsegaye Kebede of Ethiopia (2:06:04) and women’s champion of Priscah Jeptoo of Kenya (2:20:15) to the back-of-the-pack charity runners. “Go Boston!” was a popular refrain when runners wearing a Boston hat or T-shirt passed by.

“Our thoughts are with Boston,” said Melanie Burns of Petersfield, England, as she watched the elite women pass by Parliament Square. “It actually makes you more determined to come out and come out fighting.”