By JAY COHEN AP Baseball Writer

CHICAGO (AP) — When Justin Steele got hurt on opening day, the big question for the Chicago Cubs centered on the state of their rotation without their ace left-hander.
That concern faded away over time.
Steele returned to one of baseball’s best rotations on Monday night, starting Chicago’s 6-3 loss to San Diego in the opener of a three-game series. He allowed three hits, struck out two and walked one in 4 2/3 scoreless innings at Wrigley Field.
It was Steele’s first major league appearance since he strained his left hamstring while making a play on a sacrifice bunt at Texas on March 28.
“Felt really good, especially pitching at Wrigley again in front of the fans,” Steele said. “Really awesome just to be back with the team again, you know, in the locker room, hanging out with the guys and stuff. … As far as how I felt and stuff, felt really good.”
The 28-year-old Steele was a breakout performer last year, going 16-5 with a 3.06 ERA in 30 starts. He made the NL All-Star team for the first time and finished fifth in balloting for the NL Cy Young Award.
Steele made a rehab start with Triple-A Iowa on Wednesday, allowing three runs and six hits in 3 1/3 innings. He threw 68 pitches against San Diego, 43 for strikes.
“We got to build up some endurance still,” manager Craig Counsell said. “But for where we were at, I thought he delivered a great performance. Exactly what we needed, and a great first step.”
Keegan Thompson was optioned to Iowa to make room on the roster. Thompson is 1-0 with a 3.38 ERA in seven relief appearances for Chicago this season.
The Cubs have a 21-15 record, more than holding their own while Steele was out.
The rotation has played a key role in Chicago’s solid start. Shota Imanaga, who pitches on Tuesday night, is 5-0 with a 0.78 ERA in his first big league season after signing with the Cubs in January. Jameson Taillon (3-0, 1.13 ERA) and Javier Assad (3-0, 1.66 ERA) have been terrific, and young right-handers Hayden Wesneski and Ben Brown also have provided some valuable innings.
“I think our starting pitching has been excellent,” Counsell said. “Obviously some of the guys that were in the rotation all year, Shota and Javy, have been brilliant, and Jameson Taillon’s been excellent, and then Hayden and Ben have come up and been really important.”
Chicago’s starting pitchers have tossed 23 scoreless innings over the last four games. The rotation has a 3.04 ERA on the year, ranking third in the major leagues.
“I think all those guys have stepped up and really produced for us,” president of baseball operations Jed Hoyer said. “And that’s what you need to get through injuries.”