Pitching in a competitive game for the first time in almost a year since undergoing Tommy John surgery last summer, De La Rosa scattered a pair of hits over three scoreless innings in the Class A Advanced Modesto Nuts' 10-1 victory over the Visalia Rawhide. He struck out four and walked one.
"He gave us three solid innings and threw the ball well," Modesto pitching coach Darryl Scott said. "The ball came out really well. I had not seen him since Spring Training, but he has made some nice adjustments.
"It was predominantly fastball-changeup with a few breaking balls to get a feel for it. It was maybe 60 percent fastball and 30 percent changeup. His fastball was probably right in that 91- to 92-mph range."
The left-hander has been sidelined since May 24, when he left a start for the Rockies with elbow soreness. Tests revealed De La Rosa suffered a complete tear of the ulnar collateral ligament in his throwing elbow and season-ending surgery was required.
On Wednesday, the 31-year-old used an inning-ending double play to erase a leadoff single and a one-out fielding error in the first frame, and he worked around a two-out walk to Keon Broxton in the second after recording back-to-back strikeouts to start the inning.
After being hit in the glove hand by a sharp line drive off the bat of Garrett Weber in the third, De La Rosa surrendered a two-out base hit to Eric Groff. But he retired Chris Owings on a fly ball to right field to complete his night.
Scheduled to throw five innings or 65 pitches, De La Rosa was removed from the game for precautionary measures after his 45th pitch. He threw 20 more pitches in the bullpen before heading into the clubhouse.
"We just wanted to make sure there were no issues there," Scott said. "We're not sure of the extent of [the injury], but he was able to go to the bullpen and finish up his pitch count. That way he could keep his arm moving."
The 6-foot-1 native of Mexico -- who last pitched in the California League with High Desert as an 18-year-old in 1999 -- may return as early as June or early July if he experiences no further setbacks.
Scott said he expects De La Rosa to make his next start with the Nuts on regular rest, which would be in Bakersfield on Sunday or at home to San Jose on Monday. He is expected to throw 75 pitches.
"That was the plan going into it," Scott added. "Things can change, but right now we're expecting him to be with us next week. Typically in a situation of a rehabilitation, the pitch count would go up in increments of 10."
De La Rosa initially thought he could avoid surgery completely, but team doctors advised him to proceed with the operation and then begin his rehab at the start of 2012.
He began throwing bullpen sessions in early January and progressed to live 45-pitch batting practice sessions a week before the season began. On April 21, he threw four innings in an extended spring training game without any issues, and he followed that up with a six-inning outing last Friday.
A veteran of eight Major League seasons, De La Rosa has a career 54-49 record and a 4.90 ERA between the Rockies, the Kansas City Royals and the Milwaukee Brewers.
Before the elbow injury ended his 2011 season, De La Rosa was 5-2 with a 3.51 ERA and 52 strikeouts over 59 innings.