As the postseason approaches, the Atlanta Braves still are trying to lock down their pitching plans.

They'll get another good look at a candidate to start in the playoffs when left-hander Martin Perez faces the host Chicago Cubs on Tuesday night.

Atlanta (88-63), which is in first place in the National League East, will look to even the series after falling 7-3 in Monday's opener.

The Braves' magic number to clinch a playoff spot is four.

Perez (8-9, 3.08 ERA) earned a no-decision after throwing seven shutout innings in his last start against Tampa Bay on Thursday in a game Atlanta won 3-1.

Perez is 0-2 with a 5.40 ERA in three appearances (two starts) vs. the Cubs in his career. The sole relief outing came earlier this season, when he threw one scoreless inning in Atlanta's 4-1 win over Chicago on May 13.

Roster spots and roles still are in flux for the Braves' pitching staff. Manager Walt Weiss told reporters after the series opener that Monday's starter, Reynaldo Lopez (shoulder), likely would head to the injured list and confirmed that fellow right-hander JR Ritchie will come up from Triple-A and start Wednesday's finale in Chicago.

AJ Smith-Shawver is another young pitcher who will get a chance to earn a spot on the postseason roster. He impressed Weiss as he closed out Monday's loss with a five-inning relief appearance, allowing two runs.

"I always talk about the importance of starters and having options," Weiss said when evaluating the best fit for Smith-Shawver for the remainder of the season. "If we keep him stretched out, he's still an option (to start)."

As the Braves ponder their potential playoff roster construction, Chicago is part of a heated battle in the National League wild-card race.

With Philadelphia idle, the Cubs (84-67) picked up a half-game on the Phillies and took sole possession of the top wild-card spot on Monday.

With Chicago on course to make its second postseason in three years under manager Craig Counsell, pitcher David Peterson credits the skipper for his role in building a winning culture.

Peterson joined in a trade from the New York Mets in late June, but he's already seen the impact of Counsell's leadership.

"It starts with (Counsell) and the preparedness that he has, the selflessness that he has, and making sure that every guy on the team is put in the right position to succeed," Peterson said.

"I think that trickles down. It trickles down to the coaching staff, and I think it trickles down to us."

Right-hander Kevin Gausman (9-12, 4.60 ERA) will start for Chicago on Tuesday.

Gausman was the losing pitcher in the Cubs' 8-6 defeat to the Milwaukee Brewers on Wednesday. He allowed seven runs (six earned) in a four-inning stint, with Christian Yelich, Jackson Chourio and William Contreras homering.

"I just need to pitch better," Gausman said after the outing. "It comes back to execution. I can't throw lazy changeups in the zone -- those are always going to get beat."

Gausman will get another test in this start against Atlanta, the team he played for from 2018-19.

Gausman has a 1-2 record and 3.13 ERA in five career starts against the Braves. He faced them on June 2 while still a member of the Toronto Blue Jays, taking the loss after allowing four runs in six innings.