CHICAGO — The numbers are growing more ridiculous with each start, and the Chicago Cubs are running out of ways to describe the brilliance of Jake Arrieta.
The ace right-hander pitched seven dominant innings and homered in his major league-best 21st win, and Chicago stopped Pittsburgh's eight-game win streak with a 4-0 victory over the Pirates on Sunday night.
"No doubt in my mind he's the best right-handed pitcher in the game right now," catcher Miguel Montero said.
Arrieta (21-6) retired his first 18 batters before Gregory Polanco grounded a leadoff single into left field in the seventh. He struck out nine and walked none while improving to 15-1 with a dazzling 0.89 ERA in his last 19 starts.
"The finish on the pitches from the side is incredible," Cubs manager Joe Maddon said, "meaning the carry into the catcher's glove, the carry on the fastball, the break on the cutter-slider — whatever he wants to call it — it's just the finish on the pitch and you can see the hitter's reaction, it's incredible to watch."
Pittsburgh (95-61) and Chicago (90-65) each have clinched a playoff spot and lead the NL wild-card standings, so the Pirates could see Arrieta again in the first game of the postseason on Oct. 7. But they likely would have Gerrit Cole for that one — the All-Star pitched seven crisp innings in a 3-2 victory over the Cubs in the series opener on Friday.
Arrieta improved to 6-1 with a 1.68 ERA in nine career starts against the Pirates.
"I think I feel the same way against any team," he said. "I don't put a lot of emphasis on who it is."
Of course, Pittsburgh still has a chance to catch St. Louis for the NL Central title. The Pirates trail the Cardinals by three games heading into a three-game set against the division leaders beginning Monday night in Pittsburgh.
A.J. Burnett (9-6) pitched six effective innings in the season finale against the Cubs, but Arrieta shut down the Pirates right from the start. Pedro Alvarez's leadoff fly ball to left in the sixth was Pittsburgh's first ball to leave the infield.
Kris Bryant had an RBI single in the first for Chicago, and Arrieta made it 2-0 with a one-out drive to right-center in the second. Arrieta's second homer of the season led to a curtain call for the crowd of 40,617 at Wrigley Field.
"He can hit. I left one over and he hit it," Burnett said. "The ball came right over the plate, and he put a good swing on it."
The Pirates threatened after Polanco's single in the seventh. Arrieta hit Andrew McCutchen with one out, putting runners on first and second, but Ramirez bounced into an inning-ending double play.
Starlin Castro hit a two-run double in the bottom half, and Travis Wood finished the one-hitter for his third save in three chances. Castro, Bryant and Montero had two hits apiece for the Cubs.
Ramirez received a standing ovation when he was recognized by the Cubs during a pregame ceremony. Ramirez played for Chicago for nine years, batting .294 with 239 homers and 806 RBIs, and plans to retire after this season.
Castro, who played with Ramirez, presented the slugger with the No. 16 from the Wrigley Field scoreboard.
Cubs 1B Anthony Rizzo has missed just one game this season, and Maddon is weighing the value of a day off.
The regular-season finale is next Sunday at Milwaukee, and then there are two off days before the wild-card game on Oct. 7.
"Before you get to that game, he's going to have plenty of rest," Maddon said. "So, again, I don't want to take him out of a rhythm of sorts."
Burnett struck out Jorge Soler in the first for the 2,500th strikeout of his career.
Pirates: LHP J.A. Happ (6-2, 2.28 ERA) and Cardinals RHP Lance Lynn (12-10, 3.16) face off in the series opener. Pittsburgh and St. Louis split their first 16 meetings of the season.
Cubs: RHP Kyle Hendricks (7-7, 4.23) gets the ball when the Cubs host Kansas City on Monday in their final scheduled home game. RHP Yordano Ventura (12-8, 4.40) starts for the Royals in the makeup of a May 30 rainout.
Jay Cohen can be reached at http://www.twitter.com/jcohenap