CHICAGO -- Jason Heyward's reboot paid big dividends for the Chicago Cubs on Sunday.

The Cubs right fielder went 3-for-6 with three RBIs -- including a game-winner in the 13th inning -- in a 3-2 come-from-behind victory over the San Francisco Giants.

And Heyward says there's more room for improvement as a late season revival picks up steam.

"I feel like it's still coming, I feel like I've had flashes of it," said Heyward, now batting .307 in his last 13 games since sitting out a weekend series last month. "But either way, it's just one day at a time. Keep competing and keep trying to do something every game. That's the bottom line."

The Cubs (88-48) took three of four from the Giants (73-63) in a potential National League playoff preview that featured four straight one-run games.

Heyward lined a run-scoring base hit to center off Giants reliever Matt Reynolds to score Anthony Rizzo from second base in the Cubs' sixth come-from-behind win of the season.

Rizzo reached on a leadoff single to left center and advanced to second on Ben Zobrist's infield ground out. With first base open, the Giants intentionally walked Addison Russell and set up Heyward's heroics.

Reynolds (0-1), the 10th Giants' pitcher of the day, took the loss. Trevor Cahill (4-4), the Cubs' eighth pitcher, worked one inning for the win.

The revival of Heyward, struggling at the plate much of the season and entering Sunday with a .231 average, could be traced to a weekend off in Colorado.

"When a very good major league player may be struggling, if he just sits and watches a major league game being played and understands (he's) one of the best at doing this," Cubs manager Joe Maddon. "(Now) he's more on-time with everything."

San Francisco (73-63) remained two games behind the National League West-leading Dodgers while still atop the wild-card standings.

"You hate losing three out of four here, especially one-run games," Giants manager Bruce Bochy said. "We ran into a very good club, a very good pitching staff and (we) were scratching, clawing for runs. We just couldn't close it out today. But I'm good with how they played and how hard they played this series."

Giants starter Johnny Cueto settled for a no-decision despite allowing one run on five hits in a sharp seven-inning outing.

"I just came out and did my job, same as always," Cueto said through a translator. "I felt really good. I was putting the pitches where I wanted to."

Cubs starter John Lackey, back in the rotation after a stint on the disabled list, also had no decision in his first start since Aug. 14.

Cueto struck out five and walked just one as he settled for his fourth no decision since Aug. 3.

"I felt pretty good, I was locating the ball pretty well today," he said. "We had a good mix going, Willie (catcher Willson Contreras) and I."

Lackey missed 19 games during a stint on the disabled list with right shoulder strain. He allowed one hit, two runs (one earned) while striking out four and walking one.

The Cubs erased a 2-1 Giants' lead in the ninth as Russell had a leadoff double to the left-field corner, took third on a wild pitch and scored on Heyward's single to center.

The Giants threatened in the 11th with runners on second and third with two outs. Cubs closer Aroldis Chapman, however, wrapped up a two-inning relief outing by striking out Brandon Belt.

The Giants opened a 1-0 lead on a second-inning unearned run as Belt walked, reached third on Jarrett Parker's infield groundout to Lackey and came home on Eduardo Nunez's ground out to short.

The Cubs made it 1-1 in the fourth with two out when Rizzo scored from third. He walked to open the inning, moved to second on a walk, reached third on Russell's double play grounder and scored on Heyward's single to left.

The Giants reclaimed the lead in the fifth as Nunez doubled to right with one out, stole third and scored on Ehire Adrianza's sacrifice bunt.

NOTES: Sunday's game was the Giants' league-leading 48th one-run game of the season. San Francisco is 5-13 in one-run contests since the All-Star break. ... Manager Bruce Bochy said the Giants aren't planning to call up any more players to their expanded September roster. ... The Giants send RHP Matt Moore (9-10 3.88 ERA) against Colorado's Chad Bettis (11-7, 5.17 ERA) in the opener of a three-game series on Monday at Coors Field. ... Manager Joe Maddon said Sunday that RHP Hector Rondon could rejoin the Cubs sometime on the upcoming road trip and that the club might add some minor league call-ups later this week. ... Cubs RHP Kyle Hendricks, who is the National League pitcher of the month for August, brings a 13-7 record and NL-lowest 2.09 ERA into Monday's start at Milwaukee against Brewers RHP Zach Davies (10-6, 4.07 ERA). It's the first contest in an nine-game, 10-day road trip that takes them to Houston and St. Louis.