CINCINNATI — No. 1 for Aroldis Chapman. Eight and counting for his new team.

The Cuban left-hander hit 103 mph on the radar gun during another sizzling inning Wednesday night, then got his first big-league win when the Cincinnati Reds rallied for a 6-1 victory over the Milwaukee Brewers that pushed their NL Central lead to eight games.

Big numbers all around.

The Cuban left-hander threw two pitches that clocked 103 mph — his fastest yet — in his second straight unhittable performance.

“I’m really happy to have my first win,” Chapman said, through a translator. “I’m very proud of it. I didn’t have any expectations about coming to the major leagues. I just wanted to get here and stay here.”

Now, the Reds take their 22-year-old pitching sensation on the road for the first time, heading to St. Louis for a weekend series that’s less of a showdown and more about survival for the defending champs.

“There’s more pressure on them than there is on us,” said right-hander Bronson Arroyo, who will start Friday. “So we can go in and play good baseball, try not to get in any kind of scuffles, and hopefully leave one game better.

“We’ve got a bigger lead than we could have ever asked for at this point in the season. We’re better than we wanted to be.”

And they’ve got Chapman to help them stay there.

The Reds trailed 1-0 when he came on and got the radar gun and the crowd rocking during a 1-2-3 seventh inning. In his first two big-league appearances, Chapman has retired the six batters he faced, fanning three — all on sliders. He has thrown 19 pitches in all, 10 of them clocked at triple digits.

His latest three-figure performance seemed to do more than just thrill the crowd.

“That was probably another factor,” Brewers manager Ken Macha said. “He comes in and pitches an inning and energizes the crowd, everybody.”

When the left-hander jogged to the mound on Wednesday, one fan held up a sign proclaiming: “Chapmania.”

Not even close. Only 19,218 fans showed up Tuesday to watch his radar-busting debut. A day later, the crowd was down to 16,412.

Sounded louder once Chapman got going. And it stayed loud in the bottom of the seventh, when the Reds sent 11 batters to the plate for six runs. Ryan Hanigan’s pinch-hit, three-run homer in the seventh off Todd Coffey (2-3) set up the Reds’ three-game sweep.

“That seems to be the story of the season for us,” said left-hander Chris Narveson, who turned the 1-0 lead over to the bullpen. “A lot of times we’ll have a game where we feel we have control and all of a sudden — boom — it will get out of control.”

St. Louis swept a three-game series in Cincinnati from Aug. 9-11, getting the best of everything except a brawl incited by second baseman Brandon Phillips’ derogatory comments. The sweep left the Cardinals a game ahead with a 10-5 mark against Cincinnati.

Since then, everything has changed.

The Reds had the best record in the majors during August. The Cardinals have melted down, losing 13 of their last 16 games while sliding out of the race. Their final series with the Reds represents perhaps their final chance to get back into it.

“We’re trying to build on it,” Hanigan said. “We can’t take anything for granted. We’re not comfortable yet.”

Phillips was out of the starting lineup for the sixth straight game Wednesday because of a bruised right hand. Manager Dusty Baker said he could be back in the lineup in St. Louis.

Cardinals fans won’t get a chance to boo starter Johnny Cueto, who kicked pitcher Chris Carpenter and catcher Jason LaRue during their brawl in Cincinnati. Cueto got a seven-game suspension, forcing him to miss a start. He gave up five hits and one run in six innings on Wednesday before turning it over to Chapman.

NOTES: The Brewers called up 3B Mat Gamel, RHP Carlos Villanueva and RHP Jeremy Jeffress, a first-round pick suspended twice for violating baseball’s drug policy. … The Reds called up 1B Yonder Alonso, C Corky Miller and RHP Carlos Fisher. … RF Jay Bruce missed a second straight game with a sore right side. … SS Orlando Cabrera, on the DL since Aug. 2 with strained abdominal muscles, began a rehab stint in the minors. He could rejoin the team for the weekend series in St. Louis. … It was Hanigan’s first career pinch-hit homer.