SAN FRANCISCO -- The Mets have already seen their share of turmoil this season. From the dismissal of hitting coach Dave Hudgens to the demotion of franchise catcher Travis d'Arnaud, they have been forced to confront their own failings.

Yet for all of their troubles, the Mets began play Sunday just five games out in the National League East. It's the only message that manager Terry Collins hoped to drive home, even with his team in the midst of a tailspin.

Their run of futility continued on Sunday, when Giants claimed a 6-4 victory, forcing the Mets to endure their second straight three-game sweep.

After taking four of five from the Phillies to begin this road trip, the Mets found themselves on the receiving end of a sweep to the lowly Cubs before they were treated to the same fate against the surging Giants.

Curtis Granderson homered twice, finishing 3-for-4 with a double and three RBIs, though his performance alone wasn't enough to spare his team from its sixth consecutive loss. Granderson recorded the 15th multi-homer game of his career, his first since Oct. 3, 2012 while with the Yankees. His first inning blast ended a homerless stretch of 64 at-bats.

Mets starter Zack Wheeler surrendered four runs in just 3 2/3 innings, his shortest start of the season.

He had entered his start on an upward trajectory. Plagued by command issues to begin the year, Wheeler succeeded in reversing the trend of late, lasting at least six innings in each of his previous three outings. In 19 2/3 innings, he had allowed only three earned runs, while walking three and striking out 23.

The string of starts represented a clear step forward for Wheeler, 24, who has encountered a steep learning curve in his first full season in the big leagues.

That progress was thwarted by the Giants. After the Mets took a 2-0 lead in the first, courtesy of Granderson's two-run shot to centerfield, the Giants turned the tables with a three-run second inning.

Brandon Crawford singled home Hector Sanchez before Gregor Blanco delivered the big hit. With two down, and runners on second and third, Blanco rifled a two-run double to rightfield that pushed the Giants to a 3-2 lead.

By then, it was already clear that Wheeler lacked the command he had displayed in his previous three starts.

Nevertheless, he underscored that point in the fourth, when he let a 94 mph fastball get away from him. The ball drilled Hunter Pence in the ribcage, prompting a few harsh words from the Giants rightfielder on the way to first base.

Wheeler paid for the mistake two batters later, when Pence made it 4-2 when he scored on a double-play grounder by Michael Morse.

By the fourth, Wheeler was out of the game, the final straw coming when Giants counterpart Tim Lincecum lashed a two-out single.

Twice, the Mets narrowed the gap to just one run. Twice, they failed to stop the Giants from padding their lead.

The first came in the sixth inning, when Granderson hit a solo shot that nearly plunked a kayaker in McCovey Cove. But reliever Carlos Torres gave the run right back in the seventh on Blanco's single up the middle to score pinch-hitter Ehire Adrianza.

The second came in the eighth inning, when the Mets used a two-out rally to trim the Giants' lead to 5-4. With runners on second and third, Giants manager Bruce Bochy summoned reliever Jean Machi, owner of a 0.32 ERA. But Machi gave the Mets a break, throwing a wild pitch that allowed Murphy to score.

The Giants answered with a two-out rally of their own. Brandon Crawford laced a double off lefty specialist Scott Rice, then scored on Brandon Hicks' run-scoring single against Vic Black.

Notes & quotes. David Wright struck out as a pinch-hitter in the seventh inning. Sunday's series finale was the first time all season that Wright did not start . . . Reliever Gonzalez Germen (virus) is nearing a return from the disabled list.