CHICAGO – Royce Lewis became the first player in major league history to hit four grand slams within 18 games, but the way he has improved his plate discipline may be just as impressive to his coaches.

Since returning from a stint on the injured list with an oblique strain on Aug. 15, Lewis entered Saturday with a walk in 12.2% of his 123 plate appearances and a strikeout in 18.3% of his plate appearances. Contrast that with a 3.0% walk rate before his stint on the IL with a 28.3% strikeout rate.

Lewis noted he drew only three walks in his first 99 plate appearances this year. He drew three walks Friday.

"His aggressiveness is something that is really a strength of his, but he's learning how to temper it," Twins hitting coach David Popkins said. "Understand in certain counts, guys are throwing pitches that are more likely to get you to chase because they know you're not going to walk."

What makes the 24-year-old Lewis unique is he can quickly adjust in each of his at-bats. It's difficult for opposing pitchers to exploit a weakness repeatedly. There are days, Popkins said, when Lewis can work on something in a single session in the batting cage and immediately apply it in games.

"Usually, [opposing] teams will adjust, and then you go through a little lull, and you figure it out again," Popkins said. "They've been doing that, and he's adjusting with them, which is probably one of the most rare things you can ever see in baseball. He's adjusting so quickly."

In Lewis' first 28 games back from the IL, he's batting .280 with 10 homers, five doubles and 35 RBI. He's hitting the ball harder, raising his average exit velocity from 87.7 mph before his stint on the IL to 91.5 mph.

"They throw him a couple of tough breaking pitches to start the at-bat, and it's more subtle," manager Rocco Baldelli said. "You go, 'Oh, my God, he just laid off a couple of tough pitches with two strikes and fouled a pitch off above the zone.' All of a sudden, he gets something that he can handle, and he makes it happen."

Lewis worked with hitting coaches when he was nearing a return from his oblique injury, but a lot of his improvements are just natural talent. He's played fewer than 70 games in the majors, and he totaled less than half a season in the upper minor leagues.

For Lewis, his improved plate discipline is simple. It's a bigger focus on looking for his pitch.

"If I can't do damage on it, just trying to take it," he said. "Realizing, yeah, I could probably hit that. I believe in my talent enough that I can touch it and make contact, but it's going to be a ground ball, so why? What's the point?"

Keuchel out of rotation

After the Twins inserted Bailey Ober into the starting rotation, giving their other starters an extra day between starts, they will maintain a five-man rotation.

Lefthander Dallas Keuchel, for now, is the odd man out.

Baldelli emphasized it's not a final decision. The Twins could tweak their rotation over the final two weeks of the regular season. They have two off days within a five-day span next week, and they could move starters around if they clinch a divisional title well before the playoffs begin.

"I think protecting our bullpen when possible is something we're going to have to keep an eye on," said Baldelli, who could limit relievers pitching on back-to-back days. "[Keuchel] will be available out of the bullpen, and then we'll see what the rest of the week looks like when we get there."

Keuchel made one relief appearance this season in a piggyback situation with Ober. He pitched five scoreless innings in a 13-inning victory over the Rangers.

Etc.

• Baldelli will take paternity leave after Saturday's game with his wife, Allie, set to deliver twin boys. Bench coach Jayce Tingler will serve as the interim manager. "I don't have a plan for a return yet," Baldelli said. "We'll see how Allie's feeling and how the babies are doing."

• The Saints lost 7-5 at Iowa to be eliminated from playoff contention, even though at 80-62 they have the best overall record in the International League West. They failed to win either the first- or second-half division title.