CHICAGO — A cold snap hit Wrigley Field as the Giants took batting practice, which is no coincidence when you think about it.

Instead of balmy weather and homer-happy conditions Friday afternoon, the winds suddenly changed, gusting off the lake and knocking down anything hit in the air.

For Matt Cain, it became a great day to pitch. For the rest of the Giants, it became another day to watch their season scatter in the breeze.

Cain tossed a three-hit shutout through seven innings, but Tyler Walker served up a three-run home run to Aramis Ramirez in the eighth as the Giants lost, 3-1, to continue their winless trudge to the All-Star break.

They are 15 games under .500, on pace for 94 losses and have been outscored 22-4 while losing the first four games of this big-city trip to New York and Chicago.

Cain was pleased with the personal momentum he'll take into the break following an inconsistent first half but said it won't mean much in the grand scheme.

"As a group, we've got to get going to stay in this thing," he said. "We've just got to find ways to win no matter what....We've got to get some momentum going in the second half, and we've got to win these next two games for sure for that to happen."

The Giants will not be favored Saturday, when they must defeat hard-throwing Rich Harden in his Cubs debut to avoid matching a season-worst six-game losing streak. The Giants counter with No. 5 starter Kevin Correia; they are 1-15 in games behind Correia and Pat Misch, their No. 5 starters this season.

And their offense must do better than Friday's five-hit effort, which was actually an improvement over the nine hits they managed in three games at Shea Stadium. They are batting .117 on the trip, and before back-to-back singles in the sixth, they hadn't collected multiple hits in 32 consecutive innings.

With the offense barely conscious, any pitching mistake leads to certain doom. So it went after Ryan Theriot singled off Walker to open the eighth and advanced on a sacrifice.

Giants Manager Bruce Bochy didn't like his chances of retiring Derrek Lee and Ramirez, so he ordered an intentional walk to set up the double play. But Walker didn't get his first-pitch fastball far enough inside.

Ramirez's drive curled inside the pole and bounced onto Waveland Avenue as a sellout crowd celebrated. The Cubs are 36-11 at home, lovable losers no longer.

"You're caught in a hard spot," Bochy said. "You've got two similar hitters. We're hoping we can get out of it with one pitch. That way you'll only face one of them."

Walker said: "It's a tough day and a tough stretch for us. That's not what we needed....It's not my decision who we pitch to or who we don't. It's my job to execute pitches and the 'L' is in my corner, deservedly so."

At least the loss didn't fall to Cain, who might have had his best command of the season. He allowed one hit in the first five innings — a blooper by Theriot that second baseman Ray Durham drifted under before letting it clank off the heel of his glove.

Any no-hitter controversy evaporated when Lee blooped a double in the sixth inning. Cain escaped that jam. He faced another in the seventh after Daryle Ward hit a leadoff double but pumped fastballs past Mark DeRosa and Reed Johnson to maintain the scoreless tie.

"I was feeling confident with anything we threw," said Cain, a flyball pitcher who let the breeze work for him.

Jason Marquis shut out the Giants through seven innings while giving up just three singles. Cubs closer Kerry Wood lost the shutout in the ninth on Bengie Molina's single. But Aaron Rowand struck out, and with the tying runs in scoring position, Rich Aurilia grounded out after hitting a pitch off the end of his bat.

Bochy and Walker pointed to the ninth-inning rally as evidence that the Giants aren't quitting — even if the standings suggest it might be time to start thinking about draft position in 2009.

"It's gotta get better," Walker said. "I don't think anybody here is feeling it's over. Everybody on this bench and in this bullpen is here to fight."