Matt Chapman opened the 10th with a go-ahead single, Dylan Smith capped a five-inning shutout effort by the San Francisco bullpen with a 1-2-3 bottom of the inning and the visiting Giants finished a marathon trip with a 2-1 victory over the Chicago Cubs on Sunday night.

Playing a second consecutive extra-inning affair at the end of a 10-game, three-city venture, the Giants wasted no time taking advantage of their automatic baserunner in the 10th when Chapman grounded a Trent Thornton (2-2) pitch into right field, easily scoring Jonah Cox.

Smith was acquired from the Detroit Tigers in March and pitching just his third game for the Giants after a minor league stint. The right-hander struck out Michael Conforto to open the last of the 10th with a one-run lead.

After automatic runner Pete Crow-Armstrong stole third, Smith then induced consecutive popups from Michael Busch and Alex Bregman for his first career save.

The outcome spoiled a remarkable effort by Cubs reliever Javier Assad, summoned cold from the bullpen in the second inning when Chicago starter Jameson Taillon was forced to leave with a left hamstring strain.

After allowing the Giants' only regulation run in the top of the first on an RBI single by Jung Hoo Lee, Taillon walked Chapman to start the second and summoned the trainer to the mound. He was pulled from the game, walking gingerly into the dugout and down the stairs toward the clubhouse.

Recalled Saturday from Triple-A Iowa, Assad was immediately thrust into the action and performed brilliantly. The right-hander kept the Giants scoreless for the next 6 1/3 innings, allowing just one hit and one walk while striking out five.

Giants starter Trevor McDonald was almost as good. He limited the Cubs to one run over five innings, serving up four hits and three walks. He struck out six.

Chicago's lone run came in the third, a product of consecutive two-out singles by Carson Kelly, Crow-Armstrong and Moises Ballesteros.

Giants relievers JT Brubaker, Caleb Kilian, Erik Miller and Keaton Winn (2-1) bridged the innings between McDonald and Smith, getting three outs apiece while allowing a total of three hits. Winn, who allowed a hit and a walk but no runs in the ninth, was credited with the win.

Chapman had two of the Giants' four hits, both singles, the second of which produced a walk-off win after San Francisco had a pair of last-pitch losses on their 5-5 trip.

Ian Happ had the game's only extra-base hit, a triple, for the Cubs, who completed a 2-4 homestand in which they lost series to both the Athletics and Giants.