As he approached the finish line, Keflezighi pointed to the letters U.S.A. on his chest and the crowd, already cheering, roared.
"The USA gave me all the opportunities there is in education, sports and lifestyle," he said. "To be able to represent the USA is a big thing for me."
His triumph was one of persistance after hardships two years ago that would have sidelined a lesser man: During New York's 2007 Olympic Men's Marathon Trials, he came in eight after suffering calf cramps and a fracture his right hip during the race.
"He's going to be on my mind when I run and I'm going to do the best that I can," Keflezighi said at an emotional news conference a few days ago.
He said he was preparing to run past the place where his friend died.
"I know that when I hit that spot when I'm running, I'm going to feel it," he said.
He cried after he won and said later the tears were for Shay.
Keflezighi has brought glory to his adopted country before: His second place in 2004 was the first medal won by an American in the Olympic men's marathon since 1976.
In all, six Americans finished in the top 10, making it a banner day for US running.
"Americans are back!" said race director Allan Steinfeld.
Radcliffe led for much of the race but fell to fourth toward the end. She was clutching her left leg in pain after finishing.
Tulu, 37, won Olympic running medals in 1992 and 2000.
But she hadn't won a major marathon since London's in 2001 and struggled with her weight after the birth of her second daughter three years ago.
New York's world famous marathon, always held on the first Sunday of November, winds through all five of the city's boroughs.
It attracts hundreds of world-class professional athletes and more than 100,000 ordinary runners who compete for the 37,000 spots.
The winner gets $600,000 and the cheers of two million spectators.