Welington Castillo led off the top of the eighth with a single, and after a two-out walk of Tony Campana, the ninth
-place hitter who gave the Bucs fits all night, DeJesus drilled his decisive hit to right.
The late-game see-saw of emotions left the Pirates drained and stunned. They do not play the game in a vacuum. They know the Cubs are, in general manager Neal Huntington's words, one of "the teams we're supposed to beat."
Since the All-Star break, the 86-loss Cubs have a 5-20 road record overall, and are 4-1 in Pittsburgh.
All things considered, the Pirates wish the Cubs had "gone Strasburg" with Samardzija before Saturday night.
Instead, Samardzija was given the ball one more time before being shut down for the rest of the season, and he used it to put a dent in the Bucs' playoff hopes. Pittsburgh is 1 1/2 games back in the National League Wild Card race, with the Dodgers and Cardinals in front of them.
Going all out to go out in glory, Samardzija delivered 120 pitches in the first complete game of his career, and the first complete game by a Cubs pitcher this season. Pitch No. 119 was a 96-mile fastball. That is Justin Verlander territory.
"I wanted to prove I could be the guy they needed me to be and I didn't want to leave any question marks out there," said Samardzija, a former reliever who had to lobby his way into the Cubs' rotation.
"That's a special arm over there," Pirates manager Clint Hurdle had to concede.
"He mixes his pitches well. He's got a good fastball, and he just competes well," said Pedro Alvarez, who claimed half of the four hits off Samardzija, with a two-run single in the first and a fourth-inning double. "He keeps the ball down, and makes good pitches when he needs them. Anytime anyone can do that, makes him tough to hit."
Pittsburgh's forgotten hero was Jeff Clement, whose run-scoring pinch-hit single in the seventh tied it at 3, converting a two-out throwing error by shortstop Starlin Castro. For Clement, previously 0-for-9 this season with the Pirates, it was his first Major League hit since Aug. 14, 2010.
As a backdrop, the teams engaged in a bit of throwback gamesmanship. Samardzija plunked Andrew McCutchen, the Bucs' No. 3 hitter and a noted Cubs nemesis, with his first pitch to him in the first. In the third, James McDonald nailed Antony Rizzo, the Cubs' No. 3 hitter.
Plate umpire Scott Barry promptly issued warnings to both benches, and everybody was on their best behavior the rest of the evening.
Well, with the exception of the Pittsburgh batters. They remained without a home run this entire homestand, now five games old. It is the first time all season the Bucs have gone five consecutive games without a homer.
The latest blow against the Bucs' postseason hopes was abetted by a little center fielder who batted ninth in the Cubs' batting order. Stealing a page out of Tony La Russa's St. Louis manual, Chicago manager Dale Sveum had Samardzija in the eight-hole and Campana on the bottom.
But the 5-foot-8 speedster, replacing Brett Jackson, who bruised his left knee making a daring catch of a McCutchen drive in Friday's game, singled and doubled to trigger two of the Cubs' scoring rallies, and walked to further another.
Campana thus had a lot to do with compromising an otherwise upbeat outing by McDonald, who in his prior start had allowed four Milwaukee homers in 2 2/3 innings.
"J-Mac was out there competing, and he was finishing things off so innings didn't get away from him," Hurdle said. "The one thing that complicated it for him was the leadoff man getting on in five of his six innings. He had to stay in the stretch most of the night."
McDonald went 5 2/3 innings, allowing seven hits and three runs, with two walks and two strikeouts.
The Pirates are the only NL club to have lost consecutive home games against the Cubs, and they have now done it twice. The first instance, July 23-24, also featured Samardzija.
The Pirates got a reprieve from the Samardzija who had blanked them on one hit for eight innings on July 23, but it did not last long.
Brock Holt led off the first with a single and was sacrificed to second by Starling Marte before Samardzija plunked McCutchen and Garrett Jones walked to load the bases. Alvarez ripped a single to right-center to score two.
"That start, after last night, was encouraging," said Hurdle, referring to the bounce-back from a 12-2 loss. "Then we weren't able to add on."
When Samardzija ended the inning on strikeouts of Alex Presley and Clint Barmes, he signaled the return of the tough 6-foot-5 righty.
Starting with those two punchouts, he retired 19 of the next 20, up to the point that the Bucs converted a seventh-inning break into the tying run.
Tasked with guarding that early 2-0, McDonald couldn't find the shut-down mode. Alfonso Soriano immediately got one run back on a leadoff homer in the second, his 27th, and the Cubs only managed to tie it in a third begun with singles by Campana and DeJesus, on a double play off Luis Valbuena's bat.
In the fifth, Samardzija got a lead to protect. Campana led off with a double, stole third for the 122nd theft against the Pirates and scored on Valbuena's sacrifice fly.