With the numbers Gallardo is putting up, it's easy to see why.
"Yovani's makeup is pretty special," Yost said. "He doesn't get flustered very easy. The thing I like about it is that you can't tell from his demeanor what is going on. That's a little bit like Tom Glavine and Jon Smoltz. You couldn't tell if they were down 15 runs or up 15 runs."
Gallardo (2-1) gave up three hits, walked two and struck out four. He started in place of Brewers ace Ben Sheets, who was put on the disabled list Monday with a sprained right middle finger.
Gallardo has given up just six runs in 25 1/3 innings in his four starts since being called up June 14. He also has made three relief appearances since joining Milwaukee, giving up four runs (three earned) in 9 1/3 innings.
The Diamondbacks' only serious threat against Gallardo came in the fourth inning. Jeff DaVanon led off with a double down the left-field line. Orlando Hudson sacrificed DaVanon to third, but Gallardo struck out Eric Byrnes and induced Conor Jackson to fly out to end the inning.
"He's really staying on the attack," Yost said. "He's making great, great progress."
Gallardo said he did not feel any extra pressure starting for Sheets.
"I went out there and did the best I could," Gallardo said. "I felt pretty good. I made some pitches when I was supposed to."
Arizona manager Bob Melvin said Gallardo is a "pretty confident kid" on the mound.
"His fastball explodes and he really didn't have to use his breaking ball all that much," Melvin said. "He has good command of his pitches."
The Brewers also broke out of their offensive slump, scoring more than four runs for just the third time in their last 13 games.
They were led by Graffanino, who homered, scored three runs and drove in three runs. It was his eighth home run of the season, tying his career high set in 1997 with the Atlanta Braves.
"It was good for us to hit like that and score some runs," Graffanino said. "I feel like I am doing some stuff to help the team win."
Matt Wise pitched three innings to earn his first save in two chances.
Livan Hernandez (5-6) pitched 5 1/3 innings for Arizona, and was charged with six runs and eight hits. The Diamondbacks have lost eight of their last nine road games.
Milwaukee grabbed a 1-0 lead in the first inning. After Craig Counsell walked, Ryan Braun lined a shot to left that Byrnes could not handle as he tried to make a lunging catch. The ball got by Byrnes and Counsell scored. Braun ended up at second with a double.
Graffanino homered in the fourth to make it 2-0.
The Brewers broke it open in the sixth inning. Tony Gwynn Jr. hit a one-out RBI single and Counsell followed with a two-run single to chase Hernandez. Gwynn scored the final run of the inning when reliever Dustin Nippert's throw to first on a pickoff attempt got by Jackson.
Gabe Gross hit a two-run homer and Graffanino doubled in two runs in the seventh to help extend the lead to 10-1.
Jackson homered in the seventh for Arizona.
- Wise's seventh-inning single off Nippert's glove was his second career hit. The first came July 21, 2005, against St. Louis. "He got a hit two years ago and we still haven't heard the end of it," Yost said.
- The attendance was 41,156, the 16th sellout of the season for the Brewers. The team had 14 sellouts in all of the 2006 season.