"He is one of the best players in the game," manager Bruce Bochy said. "He impacts the game like few players can.
"The key to beating the Mets is keeping him under control and today we didn't."
Cain (2-4) once again showed an apparent affinity for the night time, allowing five runs in five innings to walk away with his third losing decision in six daytime starts. Under the artificial lights, Cain has a 3.50 ERA in 43 2/3 innings, but his ERA is more than two runs higher in the afternoon.
"Matt was just up too much today, especially in the first inning," Bochy said. "He had trouble getting the ball down, hitting his spots, and we got down three early."
The Giants' day started off bad and progressively got better, but, alas, in baseball, that kind of effort usually doesn't bring success.
Reyes opened the game with a double to right field and Carlos Beltran brought him and David Wright (hit-by-pitch) home with a double to center. Beltran's ball was nearly within Aaron Rowand's reach, but it sailed farther and eventually bounced off the edge of the center fielder's glove.
Rowand's day proceeded to get worse, but not before Carlos Delgado scored Beltran with a line drive single.
In the third, with the Giants (25-35) down 3-1, Rowand stepped to the plate with a chance to bring home a pair of runners. Randy Winn and Jose Castillo were on the corners when Rowand hit a ground ball that appeared that it may head through the infield. But second baseman Luis Castillo snatched the ball at the edge of the outfield grass and tossed it to Reyes for a force out to end the threat.
Earlier in the frame, Fred Lewis had scored the Giants' first run thanks in part to Reyes' gaffe. Lewis hit a soft, two-out grounder to short, but Reyes let the ball roll under his glove. Lewis advanced to second on a wild pitch and Castillo singled him home.
Neither Reyes nor Rowand were done for the day. Reyes smacked his two-run homer in the fourth to widen the Mets' lead -- a shot that scored pitcher John Maine, who reached base on a two-out walk.
"To walk a pitcher, obviously with two outs," Cain said, "no matter what is always going to haunt you. Probably the defining moment of the game."
And what about Reyes?
"You just try to make your best pitches to him," Cain said. "You try to get him out as quick as possible because you don't want a guy like that up to bat or on the bases."
Rowand, meanwhile, closed his day by getting hit by a pitch in the eighth inning. He eventually came home on a Bengie Molina sacrifice fly, but the Giants couldn't score again, finishing their six-day homestand with a 2-4 record.
Maine (6-4) scattered seven hits over six innings to earn the win, and Billy Wagner picked up his 13th save by pitching a one-hit final inning. Maine now has started eight games in which he's lasted at least six innings, while Cain's five-frame outing was his shortest since April 18.
Omar Vizquel managed to briefly bring the Giants faithful to their feet with a leaping catch, snagging Wright's liner in the seventh inning.
"He does it all the time," said Travis Denker, who had a nice day himself, going 2-for-4 with a single and a triple. "It's really cool to watch him. Any ball to that [the left] side of the field, you feel like he's going to catch."
San Francisco is headed for Washington to start a three-day series on Friday -- something for which it's probably excited. The Giants are 13-19 at home and 12-16 on the road.
"We've had our struggles here at home," Bochy said. "We get tremendous support here and guys are trying hard and that's what's frustrating."