Before Friday's series opener against the Rays, Dipoto and the Angels acquired Greinke from the Brewers in exchange for shortstop Jean Segura and Double-A pitchers Johnny Hellweg and Ariel Pena.
Greinke, 28, is 9-3 with a 3.44 ERA in 21 starts this season, posting an 8.9 strikeout-per-nine ratio in 123 innings. The American League's Cy Young Award winner with the Royals in 2009, Greinke has averaged 13 wins and a 3.38 ERA over the last five years.
Greinke will make his debut for the Angels on Sunday in the series finale against the Rays.
"It turned out to be a pretty good day, an exciting day," Dipoto said. "Obviously, we're excited to acquire a guy like Zack Greinke -- a Cy Young Award winner, an All-Star, a quality Major League pitcher at a time when they're difficult to find and to access."
The Angels have had problems at the back end of their rotation for some time now. Ervin Santana raised his season ERA to 6.00 in his last start, a 1 1/3-inning, six-run outing, and has allowed four runs or more in 11 of his 19 starts this season. The Angels haven't settled on a fifth starter, either, as Jerome Williams and Garrett Richards have been inconsistent for much of the season. The Angels' rotation as whole has a 4.66 ERA.
Greinke, who is signed through the end of the 2012 season, has thrown 200-plus innings in three out of the last four years and is on pace to do the same this season.
"It should be fun," Greinke said. "They're a great team. I think the first month they struggled, but since [then], they're one of the best teams in baseball. [They have] a lot of great players, good pitching. The pitching staff will be pretty incredible."
The deal with the Brewers was in the works for some time, Dipoto said. He had multiple discussions with Milwaukee, along with other teams, while exploring the trade market.
The Angels have not yet talked to the right-hander about signing beyond the 2012 season, Dipoto said. The only thing he's offered to Greinke was a welcome to the Angels.
"We'll cross that bridge when we get to it," Dipoto said. "For the time being, we're thrilled to acquire a player of Zack's caliber. We're excited to see him get out there and see what kind of difference he can make for the 2012 Angels. We'll worry about the rest later."
The addition of Grieinke came at a significant cost to the Angels, as Segura (No. 1), Hellweg (No. 7) and Pena (No. 14) were all ranked in the Halos' Top 20 Prospects.
Segura was called up to the Angels less than a week ago as a replacement for Erick Aybar, who was placed on the 15-day disabled list on Friday. In 94 games in Double-A this season, Segura batted .294 with seven homers, 40 RBIs and 33 stolen bases.
Hellweg, a 2008 16th-round Draft pick, was 5-10 with a 3.38 ERA in 21 starts at Double-A Arkansas this season. Pena was 6-6 with a 2.99 ERA in 19 starts at Arkansas.
"Obviously, we're giving up a fair amount to bring [Greinke] in here," Dipoto said. "That's a testament to the Angels' system and guys like Jean Segura and Johnny Hellweg and Ariel Pena. They're going to go on to do very good things, and we're hopeful that this move will be not just a short-term gain, but one that's good for the organization and the history of the Angels' organization."
Dipoto flirted with the idea of using current roster players Richards and Peter Bourjos as trade bait, but he felt they're just as much a part of the future of the Angels as they are the 2012 team. They would have been particularly painful to lose.
With four days still to go before the non-waiver Trade Deadline on July 31, time still remains for the Angels to make another move.
But in all likelihood, after acquiring a player of Greinke's caliber, the Angels are finished, Dipoto said.
"In July, if we found the ability to make our Major League club better, then we were going to act on that," Dipoto said. "I think that's what we did. I think it's another testament to the organization, to the depth of the organization and, frankly, to an owner who is willing to allow us the ability to make the moves that we feel can make a difference."
As word spread through the Angels' pregame warmups that they had acquired Greinke, players were pulling each other aside, whispering and smiling.
Torii Hunter said he didn't think a starting pitcher was necessarily a must-have before Friday, but when it comes to Greinke, the Angels aren't going to complain. At all.
"I know how he pitches. He's a bulldog," Hunter said. "He has five pitches and can throw from 92-99 [mph]. If he gets pissed off, he's throwing 100. This guy's very special. He's one of the elite pitchers in the game, and I'm excited."
Joe McIntyre is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.