The Cubs had a 2-0 lead in the sixth and the Pirates' Gregory Polanco was at second base with two outs when Starling Marte hit a comebacker to Arrieta. But his throw to first baseman Anthony Rizzo sailed for an error, and Polanco scored.
"I made an inexcusable mental mistake in the sixth inning that could've cost us the game," said Arrieta, who scattered six hits over eight innings and struck out five. "That's my one takeaway. That'll bother me for a while."
"He goosed it," Cubs manager Joe Maddon said of Arrieta's throw. "He was upset about it. We almost got it done there. He pitched beautifully once again. That play hurt, and the walk to [Pedro] Alvarez [in the eighth] hurt."
Pittsburgh rallied to tie the game in the eighth. The run in the sixth was unearned, and Arrieta's ERA now is 1.96. He has a 0.95 ERA since the All-Star break, which would be the lowest ERA after the break in Major League history.
But all of those numbers aren't important to Arrieta, who also has a no-hitter among his list of accomplishments this season. Arrieta will be a free agent after the 2017 season, but when things calm down this offseason, the Cubs will likely talk to the right-hander about a possible long-term contract. Right now, he's focused on his next start.
"That's something that's worth poring over at the end of the season," Maddon said. "I just know that Jake is really focused. It's just about Wednesday, it's about playing good on Wednesday, and that's what we're all about."
He's scheduled to start Tuesday at Wrigley Field, this time against the Brewers. If he gained anything from Wednesday's game it was that the Cubs can beat the Pirates on their turf. That may be beneficial on Oct. 7 if these two teams square off in the National League Wild Card Game presented by Budweiser.