SAN DIEGO – Brian Giles was ready for Mets starter Victor Zambrano when he faced him in his third at-bat. Giles hit a grand slam and the San Diego Padres beat the Mets 7-4 yesterday to salvage a split of their four game series.

“It was a sinker – same pitch I thought he threw me in the second at-bat that I flew out to center on,” Giles said.”I put a better swing on it this time.”

Zambrano (1-2) retired the first two hitters of the fourth inning.Then pitcher Clay Hensley singled, Dave Roberts walked, and Josh Barfield had a base hit to load the bases for Giles, who hit his fifth career grand slam.

Giles’s second homer of the season came on a full-count pitch and made it 5-0 San Diego.It was a rare sight for the Padres, whose 12 home runs are last in the National League.

“We needed a big hit, we have been missing it,” San Diego manager Bruce Bochy said.”He came through big time. It sure makes life easier when you get a big hit.”

Barfield and Vinny Castilla each had three hits for San Diego. Barfield hit a solo home run in the first and scored three times.

Zambrano gave up five runs and seven hits in four innings. He hasn’t lasted more than five innings in any of his three starts. He struck out one and walked three.

“Today, it was obviously pretty much bad game management,” manager Willie Randolph said of Zambrano. “He gave up an 0-2 home run [to Barfield], which is not what you want to do. He made bad pitches at the wrong time. He has to do a better job of managing his game.”

Hensley (1-1) worked 5 1/3 innings, allowing four runs and five hits. He walked three and struck out three in his second start this season and third of his career.

Trevor Hoffman worked the ninth inning for his third save in as many opportunities.

Mike Cameron, who was traded to San Diego by the Mets, went 0-for-3 with two strikeouts and two walks in his Padres debut. Cameron was playing for the first time since suffering multiple facial fractures in a collision with then Mets teammate and center fielder Carlos Beltran while pursuing a ball in right-center on August 11, 2005, in Petco Park.

“There is only one speed to play this game,” Cameron said about adjusting for his return. “You need at-bats to get comfortable and obviously, I haven’t gotten those. …The swings are going to come together, it is just a matter of seeing the ball well.”

The Mets scored four runs in the sixth. David Wright drove in the first run with an infield single and Cliff Floyd followed with an RBI single to right. Endy Chavez added a two-run single to center before Alan Embree struck out Kaz Matsui on a full-count pitch with the bases loaded to end the inning.

“We keep fighting back,” Randolph said. “My team plays hard all the time. We don’t give up.”