CHICAGO -- Chicago Cubs pitching coach Oscar Acosta, who helped turn around one of the NL's worst pitching staffs, resigned under pressure Thursday amid personality conflicts with manager Don Baylor.

Baylor had been expected to fire Acosta at the end of the season, but he resigned instead, effective immediately. No replacement was named, but whoever it is will be the Cubs' fifth pitching coach in seven years.

"It was something I agonized over -- personality conflicts last year," Baylor said after the Cubs 13-7 victory over the Cincinnati Reds. "I tried to put the team first. I'm always rational about a lot of things, and I was determined not to do it last year if things could change this year, if we could get a little closer in some of our thoughts.

"I just didn't see going another year."

Acosta wasn't in the clubhouse after the game and wasn't available for comment.

The move came as a surprise to the pitchers, who were outspoken in their support for Acosta. The Cubs had a 5.25 ERA last year, third-worst in the NL, and the bullpen converted just 57 percent of its saves.

This year, the Cubs have a 4.07 ERA, fourth-best in the league going into Thursday's games. They've set a major-league record with 1,304 strikeouts.

"You can see the turnaround in two years, what he's done for this club," catcher Joe Girardi said. "He's done an unbelievable job."

Jon Lieber won his 20th game Thursday, the first Cubs pitcher to reach that mark since Greg Maddux did it in 1992. Kerry Wood has regained the form that made him the NL rookie of the year in 1998, and Kyle Farnsworth has emerged as one of the league's best young relievers.

Tom Gordon, pitching for the first time since undergoing ligament replacement surgery in 1998, saved 27 games.

"You can say as a manager he has the right to do this," starter Kevin Tapani said. "But I guess we also have the right to disagree with it and look for an upfront and honest answer as to why you would want to take the guy who is ... getting results and having his group of players either meet or exceed the expectations set out before the year."

But president and general manager Andy MacPhail said Baylor is trying to do what's best for the team.

"I recognize Oscar did a very good job with the pitching, but circumstances were untenable, and there was no hope for improvement on the horizon," MacPhail said. "This will be shown over time to be in everybody's best interest."

Baylor refused to say exactly what the conflicts with Acosta were. But Acosta was an intense, hard-nosed coach who made it clear things were to be done his way.

While that approach might have rubbed some people the wrong way, his pitchers seemed to respond to it.

"What makes him such a good pitching coach is maybe what some people don't like. He preaches mental toughness and being mentally prepared for the game," starter Jason Bere said.

"Baseball sometimes isn't fair, and this is a case in point," Bere added. "What's fair and not fair and what's right is different."