Angels trade Joe Saunders for Diamondbacks’ Dan Haren

Unable to an add an impact bat, the Angels chose to upgrade their rotation Sunday when they acquired ace right-hander Dan Haren from the Arizona Diamondbacks for left-hander Joe Saunders, minor league pitchers Patrick Corbin and Rafael Rodriguez and a player to be named.

“We didn’t see a fit from an offensive standpoint we thought would make us better,” General Manager Tony Reagins said before the Angels’ series finale against the Texas Rangers.

“There are still opportunities out there, and we will be aggressive in pursuing them. We’re just looking for opportunities to improve the club. We didn’t say it had to be an impact bat.”

Saunders, who threw a gem in his last start for the Angels, allowing one run and seven hits in seven innings of a 1-0 loss to Texas Friday night, was shocked when Manager Mike Scioscia pulled him off the field during the team’s pregame stretch to inform him of the trade.

“I had no idea,” Saunders said in the clubhouse, fighting back tears. “Scioscia came out and got me, and I thought he was going to tell me I was [making my next start] on three days’ rest. Then I saw Tony in the office … it’s hard.

“It’s part of the game, it’s a business, but it’s tough leaving the guys. That’s the hardest thing, because they’re my family. I spent eight years with these guys. It’s tough.”

Haren, 29, has won 30 games over the past two seasons, trailing only two-time Cy Young Award winner Tim Lincecum, and the three-time All-Star, who could make his Angels debut against the Boston Red Sox Monday night in Anaheim, has averaged 15 wins a year over the past five seasons.

The 6-foot-5, 215-pounder, who mixes a split-fingered fastball with his fastball and breaking ball, is 7-8 with a 4.60 earned run average this season, and his 141 strikeouts is tied for the National League lead.

The Angels gave up a lot to get Haren — Saunders is one of baseball’s better young left-handers, going 33-14 in 2008 and 2009 and 6-10 with a 4.62 ERA this season, and Corbin, a lefty who was a second-round pick in 2009, went 8-0 with a 3.86 ERA in nine starts at Class-A Cedar Rapids before being promoted to Class-A Rancho Cucamonga, where he is 5-3 with a 3.88 ERA in 11 starts.

But in Haren, they acquired a front-of-the rotation starter who will be under club control through 2013. Haren is in the second year of a four-year, $44.75-million contract that pays him $8.25 million this season, $12.75 million in 2011 and 2012 and includes a $15.5-million club option for 2013.

The addition of Haren and loss of Saunders, who makes $3.7 million this season, will add a net of about $1.8 million to the Angels’ $121-million payroll.

“We felt very good about our starting five, but this is a huge opportunity for us to upgrade now and for the next couple of years,” Scioscia said. “He’s pitched in big games, he has terrific stuff, and he’s a young veteran. He gives us a deeper front end of the rotation, and that’s what every championship-caliber club wants.”

The Rangers got that kind of pitcher when they acquired Cliff Lee from the Seattle Mariners on July 9. Could Haren have the same kind of impact on the Angels as the Rangers, who entered Sunday night’s game with a six-game lead over the Angels in the American League West, expect Lee to have?

“He has that potential,” Reagins said. “Cliff Lee is a dominant pitcher. We’re not expecting Haren to be the guy. We expect him to do what he does, which is give you a quality start every time out and help us reach our goal.”

Though Haren is having one of the best offensive seasons ever for a pitcher with at least 50 at-bats, hitting .364 (20 for 55) with one homer, six doubles and seven runs batted in, he will not bat in the American League.

And he will not provide an offensive boost to a team that lost its best hitter, first baseman Kendry Morales, to a season-ending leg injury in late-May. The Angels hope to add a slugger such as Washington’s Adam Dunn, but the price in prospects appears too high.

“We got a good pitcher, but it’s not Kendry Morales,” Angels center fielder Torii Hunter said. “I don’t see many players out there like Kendry, so you have to get some pieces, put them together and put them out there, and that’s what they’re doing.”

Haren’s ERA is high for him, but he’s playing on a last-place club that is 21 games out of first place in the National League West and has struggled defensively and in the bullpen.

“It’s tough to get motivated when you know you’re going to lose,” Hunter said. “Having a good chance to win, he’ll be right where he needs to be here. Dan Haren is a proven pitcher, an All-Star. He was pitching in a hitter’s park. Coming here will be a lot better for him.”

mike.digiovanna@latimes.com