Struggling to beat the top teams in the NL is one thing. Being blown out by one of the worst should only raise the level of concern for the San Francisco Giants.

Fresh off a lopsided defeat to the Colorado Rockies, the reeling Giants try to avoid a seventh consecutive loss Friday night at Coors Field.

Prior to this series, San Francisco (69-65) endured a 5-11 stretch against St. Louis, Pittsburgh, the Chicago Cubs and Los Angeles Dodgers. The Giants, though, had reason to believe they could turn things around starting Thursday in the first of 22 straight games against clubs with losing records.

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However, Colorado (55-78) scored four times in the first and Carlos Gonzalez recorded his second straight two-homer game to hand San Francisco an 11-3 loss.

Falling farther back in the NL West and wild-card races, the Giants are mired in their third skid of at least six games. They've dropped six straight and 13 of 15 on the road.

"It's uphill time," manager Bruce Bochy told MLB's official website. "We know what's ahead of us. You don't back into the postseason from where we are."

Following three consecutive one-run losses at Dodger Stadium, San Francisco yielded 19 hits and committed two errors Thursday. Loser Ryan Vogelsong hit a two-run homer for the Giants, who have totaled 14 runs in the last six.

San Francisco has lost the last four starts by Chris Heston (11-8, 3.56 ERA), who struggled in his return from a week-long stay at Triple-A Sacramento during which he never pitched. The right-hander gave up five runs and nine hits in 3 2-3 innings of Sunday's 7-5 loss to the Cardinals to fall to 0-3 with a 5.79 ERA in five August starts.

He hasn't fared any better while going 1-1 with a 9.82 ERA at Coors Field this season.

Gonzalez is 1 for 6 against Heston but has recorded back-to-back two-homer games for the second time this year while going deep a career-high and NL-leading 35 times.

''We've seen stuff like this from him before. I don't know about at this level,'' manager Walt Weiss said. ''It's pretty impressive right now what he's done, especially recently. We know all about the talent. When he gets rolling it's something to see.''

DJ LeMahieu is 6 for 9 when facing Heston and Charlie Blackmon is 5 for 9 with two home runs. Blackmon is batting .404 during a 14-game home hitting streak.

Jorge De La Rosa (8-6, 4.40) tries to help Colorado win three straight for the first time since a four-game run July 9-12. The left-hander struck out seven in six-plus innings before being ejected for arguing with home plate umpire Jeff Nelson in Sunday's 5-0 victory at Pittsburgh.

''I've seen this guy pitch for years and he challenges your discipline," Pirates manager and former Rockies skipper Clint Hurdle said about De La Rosa, who went 2-2 with a 2.87 ERA in six starts last month. "Added and subtracted velocity and spin. It's what he does."

De La Rosa yielded two runs and struck out seven in five innings of a 5-4, 11-inning home loss to San Francisco on April 25.

A lifetime .300 hitter against De La Rosa, Buster Posey is batting .483 in his last seven games.

Giants shortstop Brandon Crawford could miss a fourth straight game with a sore calf.

Concussion symptoms and a cervical neck strain have kept Colorado's Justin Morneau out since May 13, but he could return in this series.