"I didn't really have an off speed pitch today, just didn't have a good feel for my curveball," said Lester, who had 14 strikeouts in his last full outing on July 29. "(But) I was able to locate the heater effectively enough to get though seven."
Lester allowed two runs on six hits in a strong seven-inning outing while Cubs batters backed him with a 12-hit attack in a 7-3 victory over the Giants on Friday.
The win was the eighth in nine games for the Cubs (60-48) and second straight in the showdown series between National League wild card contenders.
The Cubs shuffled their infield on Friday after benching shortstop Starlin Castro. Addison Russell switched from second to short, Chris Coghlan, usually an outfielder, played second and rookie backup catcher Kyle Schwarber moved to left field.
"Coghlan had a nice day at second base, made his plays cleanly and swung the bat really well with two hits," Cubs manager Joe Maddon said. "Schwarber was outstanding ... and Addison had a wonderful day at shortstop with a tag play on a stolen base and a play from Jonny (Lester) on a double play."
Chicago is now a season-high 12-games above .500. The Giants (59-50) suffered their second loss in-a-row.
Lester (7-8) also struck out three and walked two in his second straight win and third since July 19.
"A little bit of a grind, but at the end of the day a win's a win," Lester said.
Cubs right-hander reliever Hector Rondon worked 1 2/3 scoreless innings for his 18th save.
Giants right-handed starter Ryan Vogelsong (7-8) took the loss after working just four-plus innings. It was his first start since July 11.
"I really thought he threw well," Giants manager Bruce Bochy said. "He had good stuff, he threw a lot of pitches that could have gone either way. He was right there and I was a little worried about his stamina at the end -- he hadn't started in a while -- (but) he was hitting his spots and a lot of close pitches."
The Cubs jumped out 1-0 in the first on second Coghlan's RBI single to right center drove in Schwarber, who had doubled to the wall in left-center.
Giants shortstop Brandon Crawford singled in Posey from second base with one out in the second to even the score.
Vogelsong departed after giving up back-to-back doubles with none out in the fifth to Russell and Fowler.
Vogelsong was responsible for two more runs after left-handed reliever Jeremy Affeldt gave up a two-RBI infield single to Schwarber.
Affeldt walked Cubs third baseman Kris Bryant with two out and departed for right-hander Yusmeiro Petit.
Right fielder Jorge Soler then doubled to deep left to score Schwarber and Bryant and catcher David Ross singled to center to drive in Soler for a 5-1 lead.
Vogelsong allowed three runs on six hits, struck out six and walked one in four-plus innings of work.
Lester gave up one run in the seventh as right-fielder Hunter Pence singled home third baseman Matt Duffy with none out.
But Lester got Crawford to ground into a double play and escaped further damage when pinch hitter Ehire Adrianza had an inning-ending infield popup.
Cubs right-handed reliever Tommy Hunter entered in the eighth and was greeted by left fielder Nori Aoki's pinch-hit solo home run that cut the Cubs lead to 6-3.
Fowler added an insurance run in the eighth, a two-out solo homer run to make it 7-3.
NOTES: Giants RHP Ryan Vogelsong got the start after RHP Mike Leake was scratched with a left hamstring strain this week. The Giants placed Leake on the 15-day disabled list. The Giants recalled LHP Josh Osich from Triple-A Sacramento to take Leake's roster spot. ... San Francisco was averaging 4.98 runs per game on the road entering Friday, second best in the big leagues behind Toronto (5.04). ... Giants SS Brandon Crawford entered Friday with a career-high 19 homers, as many as he has hit in the two previous seasons combined. ... San Francisco RHP Matt Cain (2-2, 4.91 ERA) will go against Chicago RHP Kyle Hendricks (5-5, 3.67) on Saturday. ... The Cubs activated C Miguel Montero (left thumb sprain) from the 15-day disabled list and optioned OF Matt Szczur to Triple-A Iowa. Szczur was batting .217 in 36 games for Chicago this season. ... Chicago also benched All-Star SS Starlin Castro in favor of rookie Addison Russell, who moved over from second base. Castro, a .278 lifetime hitter, was batting just .236 this season. ... The Cubs' 5-4 win over the Giants on Thursday was their 59th win in 107 games. In 2014, they didn't reach 59 wins until their 131st game, on Aug. 26.