The field is deep with former champions Martin Lel, Felix Limo and Khalid Khannouchi racing alongside world record holder Paul Tergat, Olympic champion Stefano Baldini and New York City Marathon winner Marilson Gomes dos Santos, the field is deep.
The calculations for a winner don't even include Haile Gebrselassie, a two-time Olympic and four-time world 10,000-meter champion who finished ninth in London last year.
"You're trying to get the best out of yourself. To do that, you race
against the best," Keflezighi said.
"This (field) is deeper than the Olympics."
Keflezighi's main concern Sunday will be his left foot injury, a bad blister he suffered in March after winning a 15-kilometer race in Florida which required him to take a two-week break from running.
"I felt it a little today," Keflezighi said.
"I was a little on my toes."
Khannouchi, who was born in Morocco but now races as an American, has set two marathon world records, but he too has had foot injuries and said he was still cautious with his training.
"I'm ready to compete," said Khannouchi, who set his second world record in London in 2002.
"The priority is to win, and if it comes with a good time, it's a great bonus."
Tergat holds the men's record at 2 hours, 4 minutes, 55 seconds, and the recent warm weather in London could keep the field from setting a new one.
"It will be a factor," Khannouchi said.
"I try not to think about it because we'll all have the same weather."
Last year, Limo held off Lel by two seconds to win the London race, but
back problems have kept him from racing for the last seven months.
"When I started serious training I still had that fear (of re-injuring my
back)," Limo said.
"I did a lot of exercise to strengthen the back."
The field for the women's race will include world cross-country champion
Lornah Kiplagat, Berhane Adere, Constantina Tomescu-Dita, Geta Wami and Chunxiu Zhou.
Last year, Deena Kastor won the women's race. She finished fifth on Monday in the Boston Marathon.
Paula Radcliffe, a three-time London champion who set the world record of 2:15:25 at the 2003 race, will not be running this year after the birth of her daughter overtook any preparations.
The London Marathon is also worth points in the World Marathon Majors
The Boston, London, Berlin, Chicago, New York, World Championships and Olympic Marathons are part of the two-year series that will award $500,000 to the men's and women's champions.