CINCINNATI -- Jung Ho Kang couldn't recall the last time he hit a grand slam, but he believes it occurred sometime last year when he belted 40 homers in the Korean Baseball Organization.

His first as a Pittsburgh Pirate came Wednesday night and J.A. Happ allowed two runs in six-plus innings, then the Pirates held on for a 5-4 victory over the Cincinnati Reds at Great American Ball Park.

"This team has shown some resilience, some backbone, some grit," said manager Clint Hurdle. "Everyone knows what we're playing for."

Pittsburgh (83-55) took two of three in the series to increase its lead to three games over the Chicago Cubs for the National League's top wild-card spot and stayed within 4 1/2 games of first-place St. Louis in the NL Central.

Happ (9-7) gave up only three hits with no walks and 10 strikeouts.

"We tried to change the levels quite a bit tonight," Happ said. "We had a good game plan, saw some success from it and that helped build some confidence."

Third baseman Todd Frazier homered for Cincinnati (57-81) which lost to the Pirates for just the sixth time in 16 meetings.

Reds rookie right-hander Keyvius Sampson was having a fine outing before encountering trouble in the sixth when Pittsburgh loaded the bases with one out.

On Sampson's 2-2 pitch, Kang lined the Pirates' first grand slam of the season over the left-field wall, putting them ahead 5-1.

"It was a great chance for me," said Kang, via interpreter H.K. Kim. "Ultimately, I think I got lucky with that swing. I was just thinking about putting a good swing on it."

It was the seventh grand slam allowed by Cincinnati this season.

Sampson (2-4) allowed five earned runs in 5 1/3 innings with two walks and four strikeouts.

"We were going in on Kang all night and he hadn't caught up with it yet," said Sampson. "We kept the same game plan. I was trying to put it on the black but it went over the plate. Anyone can hit that. I have to execute my pitches better."

Cincinnati rallied amid some drama in the eighth.

Reds first baseman Joey Votto was ejected in the middle of his at-bat after apparently not being granted time by home plate umpire Bill Welke.

"My understanding is that Joey asked for time and Welke didn't grant it," said manager Bryan Price, who also was ejected. "That's what got it started. I know that Joey looked over to the dugout and that's my sign to get out there. He was already ejected before I could get there."

It was Votto's third ejection this year, seventh of his career.

Catcher Ramon Cabrera replaced Votto with a 1-2 count and singled for his first major league hit to load the bases. A run scored on a groundout to make the score 5-4.

Pirates left-hander Tony Watson threw 37 pitches and allowed a pair of runs in the eighth but escaped with the lead intact. Mark Melancon shut the door in the ninth for his 44th save.

Pittsburgh took a conservative approach against Sampson in the first inning, despite his 6.68 ERA.

Gregory Polanco led off with a double and was sacrificed to third on left fielder Starling Marte's bunt. Center fielder Andrew McCutchen collected his 89th RBI with a sacrifice fly, putting the Pirates ahead 1-0.

Sampson pitched Wednesday's game on short rest after lasting just three innings in his last start. He was much sharper this time around, retiring 15 of 17 following Polanco's double.

Happ struck out three straight batters in the first.

But, with one out in the second, Frazier launched Happ's 0-1 pitch an estimated 406 feet to center for his 31st home run, tying the score 1-1.

Five of Happ's first six strikeouts were looking, and more than a couple Reds batters took exception to those calls Welke.

Happ had nine strikeouts through five. He finished with 102 pitches.

"He used his cutter, slider, the changeup to keep them off balance," Hurdle said. "Ten punch outs in a night is impressive. The pitch count got where it was probably because of the strikeouts."

NOTES: Reds LF Kristopher Negron is out for the season with a torn labrum and fractured scapula in his left shoulder suffered while making a diving catch of Starling Marte's line drive in the seventh inning on Tuesday. ... Reds CF Billy Hamilton returned to the lineup and leadoff spot on Wednesday. He was reinstated from the disabled list on Tuesday. Wednesday also was Hamilton's 25th birthday. ... After an uneventful first career start at 1B on Tuesday for Pittsburgh, Aramis Ramirez was back at first for Wednesday's series finale. ... LHP Francisco Liriano struck out 10 batters on Tuesday, joining RHP Gerrit Cole as the only Pirates teammates with at least 175 strikeouts in the same season.