"Pretty good," Mattingly said. "There's a lot of moxie to that kid. He really hasn't shown any fear of anything. If I had his stuff, I wouldn't either."
"He just told me to come to work and be ready," De La Rosa said.
De La Rosa worked as a starter in the Minors, and team officials view him in that role for the Dodgers over the long-term. But the club's serious need for bullpen help was underscored on Monday night, when rookie Kenley Jansen blew a two-run lead in the ninth inning of a 4-3 loss.
As a result, the team designated Lance Cormier for assignment to make room on the roster and flew De La Rosa to Houston on Tuesday.
"[De La Rosa] has a great arm," Mattingly said before the game. "We wanted to put another quality arm out there.
"It's his power stuff. We saw it all spring. It's one of those arms you don't see very often. He has pretty good command with it. The changeup is basically dirty, and his slider is getting better and better."
After De La Rosa's impressive Spring Training, management hoped to give the 22-year-old right-hander a half-season at Chattanooga, where he is 2-2 with a 2.92 ERA, having allowed 39 hits in 61 1/3 innings with 59 strikeouts and 19 walks. He was the organization's top Minor League pitcher last year, winning the Branch Rickey Award.
De La Rosa's most recent start lasted only two innings (five strikeouts), as the club implemented an innings-reduction tactic it has used in the past to cut back innings in the first half of the year to freshen arms for the second half.
Although De La Rosa has been a starter throughout his brief career, the Dodgers are set in the rotation, with Clayton Kershaw, Chad Billingsley, Ted Lilly, Hiroki Kuroda and Jon Garland.
Mattingly said De La Rosa could also be used in a long relief role should a starter run into early trouble.
"We'll use him all over," he said. "Right now, he's stretched out. If a starter got in trouble, he could be right there. But he could be used anywhere.
De La Rosa's move to the bullpen is reminiscent of 1993, when the Dodgers took a 21-year-old right-handed rookie from the Dominican Republic, who had been a starter, and put him in the 'pen.
Pedro Martinez went 10-5 with a 2.61 ERA in 65 games as a long reliever, pitching 107 innings as a springboard to what will ultimately be a Hall of Fame career, albeit one spent elsewhere after his trade to Montreal for Delino DeShields months later.
Cormier had struggled for most of the season, compiling a 9.88 ERA in 13 2/3 innings out of the bullpen.
"With Lance, it wasn't working out," Mattingly said.