With those early struggles, the heat just wore Lopez down.
"I ran out of gas trying to work my way out [of the first inning]," Lopez said. "My pitches weren't located where I wanted, and with this kind of weather during the day, it was very tough for me.
"I was trying to cool down whenever I was on the bench, coming into the clubhouse. But when I finally made an adjustment, it was too late. We were already six runs behind."
Through the first three games of the series, D-backs starters had been able to quiet the Brewers' offense and limit the damage. Lopez was not so fortunate.
The first and second innings were mirror images of each other, as Lopez opened the two innings with an out before giving up a hit to Corey Hart, retiring Ryan Braun, walking Prince Fielder and surrendering back-to-back hits to Casey McGehee and Craig Counsell.
Each of the six runs in the two innings was scored by Hart, Fielder and McGehee. In the fifth, McGehee added a solo homer to dead center field, his eighth hit in as many at-bats.
Two innings later, McGehee added a single off D.J. Carrasco, setting a new Brewers record with hits in nine consecutive at-bats.
"That's amazing," said center fielder Chris Young upon learning of McGehee's nine straight hits. "That's special when you're hitting the ball that hard that often. I don't remember too many bloop hits that he hit. He was squaring the ball up pretty well all over the field. That's definitely special."
After a two-out hit in the ninth on Tuesday, the Brewers' third baseman followed with a home run in his first at-bat on Wednesday followed by three singles for his first four-hit game of 2010.
McGehee notched a second four-hit performance on Thursday, adding two singles, a double and another home run.
"If you would have asked me if this was going to happen after the [batting practices] I've taken the past couple of days, I'd say no," McGehee said. "It goes to show you it doesn't matter what you do at five o'clock.
"It's cool, but by no means is it going to change my approach going into Colorado. I promise I'll make another out, probably in the really near future."
Lopez (5-11) lasted just five innings -- he was the first D-backs starter in the series who did not get through the sixth -- giving up seven runs on seven hits while walking three against four strikeouts.
Brewers lefty Randy Wolf dealt with the heat a little better than Lopez. Wolf (9-9) went six innings, giving up four runs on seven hits with eight strikeouts against four walks.
"I thought I was just going to turn into a pool of sweat out there," Wolf said. "You just can't stop sweating. It's difficult to grip the ball when you're sweating that much because it's all the way down your fingertips.
"You just try to make the best adjustment you can. It was pretty miserable out there."
Offensively, the D-backs put together four straight hits to score four runs in the fourth inning for the second straight night. Only the last of the four, by Stephen Drew, was a home run this time.
That was all the offense the D-backs would muster on the day, as they stranded 12 runners, leaving the bases loaded in the fourth and eighth innings, and loading them again in the ninth on three straight walks before Drew grounded into a double play.
"We were taking a strike. It's hard to see up there, and you try to keep the pressure on the guy who's closing the game out," said D-backs manager Kirk Gibson. "It was working for a while, but Stephen got two strikes on him really quick and a tough pitch. It almost took a bad hop for us ... but you're not going to win them all.
"We did compete like we wanted to win today, and that was important for us."
While the loss was a disappointing end to the series, the D-backs head to Washington having secured their first series win over the Brewers since winning two of three from July 14-16, 2006, at Chase Field.
The series victory at Miller Park for the D-backs is their first since taking two of three from the Crew from Sept. 19-21, 2003.
"It was a good series," Young said. "We gave ourselves a chance in this last game to get the win, still; we just couldn't come through with the bases loaded a couple times. But at the same time, just to get the bases loaded, we battled back quite a bit and made a potential blowout a pretty good game."