In 2 1/2 seasons for the D-backs, Haren won 37 games while at the top of the rotation. But when the club was on its way to losing 97 games in 2010, it decided to unload the right-hander's contract.
In return, the Angels sent back Joe Saunders, who will pitch Saturday in the second game, and prospects Tyler Skaggs and Patrick Corbin.
Haren comes in winning three of his last four starts after losing four straight to open May. In his most recent outing, Haren allowed 10 hits to the Rockies over 5 1/3 innings, but minimized the damage to four earned runs in an 11-5 victory in Denver.
"The ball doesn't do as much. My cutter was OK, but my splitter was awful and I couldn't control it," said Haren, whose four earned runs were the most he allowed since May 14. "I made the most of what I had. We scored a bunch of runs, so I was able to attack them."
On the hill for the D-backs will be a right-hander with plenty of experience in the American League West. Trevor Cahill, traded from Oakland in the offseason, is coming off two outstanding starts for the D-backs.
After tossing a shutout in San Diego on June 3, Cahill defeated his old club by pitching 7 1/3 innings and giving up just two runs.
"I was probably more nervous than any other start this year," he said. "Going against the team I played for, for six years. It definitely was a little more nerve-wracking."
In two starts, both losses, against the Angels last season, Cahill surrendered a combined six earned runs in 13 innings.
Angels: Downs sits another game
The Angels stayed away from using reliever Scott Downs, who is dealing with tightness in his side, in their series finale Wednesday against the Dodgers.
"He's feeling a little better, but we'll most likely stay away from him again," Angels manager Mike Scioscia said before the game.
Downs, who has a 0.42 ERA in 24 appearances this season, hasn't pitched since Sunday against the Rockies. He tossed one inning in the game, giving up one run and a season-high three hits.
The lefty hasn't had any tests, however, and was planning on going through a pregame routine and assessing his status from there.
D-backs: Saito near season debut
Reliever Takashi Saito, who has been sidelined with a strained calf since the end of Spring Training, could be getting closer to returning.
"I'm looking for him to be healthy for an extended period," D-backs manager Kirk Gibson said with regards to what will determine when Saito is ready to return. "We've had him close and then he's got hurt. I don't want to make a move on my team right now and then have him come up here and pitch a game or two and get hurt."
To this point, Saito has pitched on a schedule, but after Thursday night, the organization will have him pitch as Reno needs. That means some nights he might warm up and not get into a game, or he may pitch in back-to-back games.
If that goes well without any setbacks, he could be activated.
Willie Bloomquist has reached base safely in 21 consecutive games.
Albert Pujols saw his streak of consecutive games with multiple hits end at seven on Wednesday, although he did collect one hit. The streak was the longest in his career.