Barry Zito lost his home-field touch at AT&T Park on Tuesday and the Giants' woes continued with a 10-6 loss to the New York Mets.
The Mets handed the Giants their 18th loss in 23 games by scoring five runs in the top of the eighth inning to break a 5-5 tie. Marlon Byrd punctuated the rally by hitting his seventh career grand slam on a hanging breaking ball from Jake Dunning.
"It just seems like every possible situation that could go wrong is going wrong," reliever Jeremy Affeldt said.
With the loss, the Giants (40-49) fell to a season-worst nine games below .500. They remained 6½ games behind the Arizona Diamondbacks for first place in the NL West.
"We're getting tested like we've never been tested before," manager Bruce Bochy said.
Zito (4-7) entered the game with a 4-1 record and 1.98 ERA at home this season, but the Mets managed to knock him around, scoring five runs on seven hits and four walks over six innings. Prior to the game, the Giants had scored five or more runs only once in 11 games.
The Giants jumped out to an early 2-0 lead in the bottom of the second when the Mets did them a favor by throwing the ball around. Hunter Pence scored from third base when catcher Anthony Recker chucked the ball into center field trying to catch Brandon Belt stealing second. Belt scored from third two batters later when he beat second baseman Daniel Murphy's throw to the plate on a Guillermo Quiroz grounder.
But the Mets tagged Zito for three runs on three singles and two walks in the top of the fourth to take a 3-2 lead.
"Walking those couple guys was the difference there," Zito said.
The Giants tied the game in the fifth when Pablo Sandoval drove in Gregor Blanco on a ground out and the Mets regained the lead an inning later when Recker homered to left-center.
Sandoval tied the game up again in the seventh by scoring Kensuke Tanaka on a sacrifice fly to center, but the bullpen gave it away by surrendering five runs in the top of the eighth.
If the game had a bright spot for the Giants, it was Tanaka's performance in his big-league debut. Tanaka was called up from Triple-A Fresno earlier in the day and he took advantage of the opportunity by robbing a potential home run in the bottom of the second, recording his first major-league hit in the fifth and scoring the tying run in the seventh.
"He just has that excitement when he plays and I think that's great," Zito said. "That's what we need - we need to have a little more fun I think when we're playing right now and just enjoy the game."