Soderling saved three match points before overcoming Michael Llodra of France, 6-7 (0), 7-5, 7-6 (6).
Monfils faced five match points in the 12th game of the final set before forcing the tiebreaker with an ace.
Federer shanked a forehand to give Monfils two match points, and the Frenchman converted the first with a service winner.
"I guess I had control over it in the third, went a break up," Federer said. "That's a disappointment there. It's a tough match to lose."
Edwards wins second straight
Edwards had total control of yesterday's race after winning last week at Texas, and now has four Nationwide victories this season.
Thatcher holds four-stroke lead
Roland Thatcher remains on track in an improbable bid to keep his PGA Tour card, shooting a 2-under 70 at the Children's Miracle Network Classic to take a four-stroke lead over Chris Stroud into the final round.
Thatcher began the week 179th on the money list and needs to win or finish alone in second at the season's final tournament to vault into the top 125 - the cutoff for full status - to retain his card.
Birdrun wins at Calder
Birdrun ($4.60) beat Duke of Mischief by 4 1/2 lengths in the $150,000 Carl Rose Classic, the finale of Calder's eight-race Florida Million for Florida-bred horses.