SAN FRANCISCO -- Marlon Byrd belted Jake Dunning's first pitch for his second career grand slam, capping a five-run eighth inning that vaulted the New York Mets to a 10-6 victory over the tail-spinning San Francisco Giants on Tuesday night.
The win, on the heels of the Mets' 4-3, 16-inning triumph Monday, allowed New York to improve its road record to 22-21, third best in the National League. The Mets have won 12 of their past 17 road games and 15 of 24 games overall.
One-out singles by Omar Quintanilla off Jose Mijares (0-2) and by pinch hitter Juan Lagares off Jeremy Affeldt got the New York eighth going in a 5-5 game. Quintanilla's hit was his third of the game.
Eric Young Jr. drew a walk to load the bases, and Daniel Murphy put the visitors on top for good with a sacrifice fly to center field.
After David Wright walked to load the bases again, Byrd greeted the right-handed Dunning with a towering drive into the left field bleachers. It was the right fielder's 14th homer of the season.
Mets left-hander Scott Rice (4-5), who faced one batter in the seventh inning and preserved a 5-5 tie, got the win.
The loss was the Giants' seventh in their last eight games and dropped the defending World Series champs into a last-place tie with the San Diego Padres in the National League West. San Francisco is 17-34 in its last 51 games, the worst record in the majors over that stretch.
The Giants scored their final run with two outs in the bottom of the ninth on pinch hitter Nick Noonan's RBI single off Carlos Torres, who pitched the final two innings for the Mets.
San Francisco outhit New York 13-12 but stranded 11 baserunners.
Both teams held two-run advantages in the game, the last time when the Mets' Anthony Recker broke a 3-3 tie with a two-run home run off Giants starter Barry Zito in the sixth inning. The homer was Recker's fifth of the season.
Zito was pulled after the sixth, having given up five runs on seven hits and four walks. He struck out five.
The Giants got their left-hander off the hook by scoring single runs in the sixth and seventh to get even at 5-all. Pinch hitter Tony Abreu's infield single, the Giants' first hit with runners in scoring position after an 0-for-5 start, and Pablo Sandoval's sacrifice fly produced the runs.
Sandoval drove in two of the Giants' six runs.
Mets starter Dillon Gee, who hadn't allowed more than two runs in six of his previous seven starts, staggered through 6 2/3 innings before, like Zito, leaving with a no-decision. The five runs he allowed were the product of nine hits and a season-high five walks. He struck out three.
Batting immediately after watching left fielder Kensuke Tanaka, making his major league debut, reach over the fence to rob Andrew Brown of a home run, the Giants took advantage of shoddy Mets defense to go up 2-0 in the second.
After inning-opening singles by Hunter Pence and Brandon Belt put runners at the corners, Belt took off for second with one out and Guillermo Quiroz at the plate. When the throw from Mets catcher Recker went into center field for an error, Pence scored.
Belt, who took third on the error, raced home with the second run of the inning when Mets second baseman Murphy, playing in, threw late to the plate after fielding a grounder by Quiroz.
The Giants' lead lasted only until Brown came to the plate again in the fourth. This time he landed one in front of Tanaka, a two-run single that scored Wright, who had walked, and Byrd, who had singled.
Quintanilla's two-out, two-strike single to center scored Josh Satin, who had walked, with the third run of the inning and put the Mets up 3-2.
Sandoval's run-scoring infield out with one out in the fifth, which came two batters after Tanaka's first major league hit, tied the game at 3.
NOTES: Tanaka, a 32-year-old who was hitting .330 in 78 games at Triple-A Fresno, was the sixth man to play left field for the Giants this season, following Gregor Blanco, Andres Torres, Francisco Peguero, Brett Pill and Cole Gillespie. ... Gillespie, 0-for-7 for the Giants this season, was designated for assignment to make room for Tanaka on the active roster. ... The Giants signed OF Jeff Francoeur, who had been designed for assignment by the Kansas City Royals, to a minor league contract and sent him to Fresno. Francoeur, a nine-year major league veteran, hit .208 in 193 plate appearances for the Royals this season. ... The Giants also placed C Hector Sanchez (strained right shoulder) on the disabled list and recalled LHP Mike Kickham from Fresno. ... Mets RHP Shaun Marcum will have surgery designed to cure numbness in his pitching hand next Monday and will be lost for the season. Marcum, 1-10 with a 5.29 ERA in 14 appearances (12 starts) this season, will be replaced in the rotation by RHP Carlos Torres once the Mets return to a five-man rotation after the All-Star break. ... RHP Gonzalez Germen was summoned from Triple-A Las Vegas to take Marcum's spot on the roster.