But the left-hander overcame all that Sunday, pitching five effective innings to earn his second win of the season in San Francisco's 6-3 victory.
"It was definitely pretty tough out there," Zito said. "It was pretty hot. I don't know what the numbers were, but it'll just wear you out."
Aaron Rowand's bad-hop single gave the Giants the go-ahead run and capped a four-run fifth inning. Randy Winn hit a two-run single to tie it, and John Bowker's two-run homer in the seventh sealed the victory. San Francisco has won the first three meetings in this four-game series.
Lastings Milledge homered and drove in two runs for Washington, which has lost seven of eight.
Zito (2-9) allowed three runs and seven hits while walking four and striking out two. He has won two of his last three decisions after an 0-8 start, although he was rocky at times again Sunday.
"Zito was OK," San Francisco manager Bruce Bochy said. "He didn't have his great command. He was all right. Sure a tough day for pitchers out there -- it was smoking."
The pitcher didn't make it easy on himself, facing bases-loaded jams in the fourth and fifth. In the fourth, the first three Nationals batters reached to load the bases, but Zito got out of it with just one run allowed.
"I didn't think [Zito] had his best stuff," Milledge said. "I think he knows that."
Zito gave up three runs in the first four innings, and the Nationals had a 3-0 lead going into the fifth. But San Francisco's offense helped Zito's cause with a four-run inning, helped by a fortunate bounce on Rowand's single that drove in the go-ahead run.
And in the field, the Giants gave Zito a boost as well. When runners were on, it was the defenders behind him that made the plays to get out of trouble. Zito had just two strikeouts, both with the bases empty.
In the third, the Nationals had runners on first and second with two outs. Milledge singled one runner home, but Elijah Dukes was caught in a rundown between first and second to end the inning.
With the bases loaded in the fourth, Wil Nieves hit a sacrifice fly to score one run, but Willie Harris grounded into an inning-ending double play. And in the fifth, after Zito intentionally walked Aaron Boone to load the bases, Wily Mo Pena grounded out.
Zito managed to finish the five innings needed for a win, but until Pena's out it wasn't a sure thing.
"He was getting close there -- real close," Bochy said. "If he loses that hitter, I'd go to [Billy] Sadler there, to be honest."
After Zito departed, San Francisco's bullpen kept the Nationals' bats quiet, allowing one hit in the final four innings. Brian Wilson pitched the ninth for his 17th save.
Zito left with the lead thanks to the Giants' big fifth inning.
Washington starter Garrett Mock, making his major league debut after being recalled from Triple-A Columbus earlier in the day, held the Giants scoreless in the first four innings, thanks in large part to three double plays.
In the fifth, however, Mock wore down.
The next batter, Rowand, hit a grounder toward shortstop Cristian Guzman, but the ball took a bad hop and ricocheted off the top of Guzman's head nearly all the way to first base, allowing Castillo to score and giving the Giants a 4-3 lead.
"As the season's gone on, we've progressively gotten better at stringing hits together and scoring runs," Rowand said, "instead of one here and one there."
Mock was optioned back to the minors after the game. The Nationals are expected to recall right-hander Tyler Clippard from Columbus to start Monday night.
Milledge hit a first-inning homer into the Giants' bullpen in left field, his fourth of the season. He also had a run-scoring single in the third.
But after the game, the Nationals were thinking about all their squandered chances.
"We just couldn't deliver," manager Manny Acta said. "We needed that hit today, and it never showed up for us."
And despite his struggles, Zito had no problem with the result.
"I'm really happy the team has won the games I've started recently," he said. "For me, individually, things could be a lot better right now. I've just got to keep my nose to the grindstone."
Nationals 1B Dmitri Young missed his third straight game with flu symptoms. ... It was the first start for Giants rookie SS Emmanuel Burriss in his hometown of Washington. Burriss is the first graduate of the D.C. public schools to reach the majors since 1981. ... Rowand was in the starting lineup after leaving Friday's game with a strained right quadriceps.