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PHOENIX -- The first-place Houston Astros and the Arizona Diamondbacks, who lead the National League wild-card race, are learning all about baseball's dreaded dog days of August.

The alarm clock seems to go off sooner. The knees ache a little more. The throwing arm takes longer to get loose. The three-hour games seem to last four. The road trips, no matter the length, seem longer and longer and longer.

The Astros and Diamondbacks finish up a two-game series at Chase Field on Tuesday, then fly off to play two more in Houston. The clubs have been in playoff position since April, but now that it is August and the end to the major league season is weeks rather than months away, the schedule is taking its toll.

"I know this is the time of the year when everybody is tired. Not physical tired. It's a mentally grinding thing," Diamondbacks manager Torey Lovullo said. "We hustle, we play hard, but at times we wander."

The Astros (72-46) have held a double-digit lead in the AL West for several months, but injuries -- they have eight on the disabled list -- and losses are starting to mount up. They have dropped 10 of 13 games this month and eight of their past nine on the road. They are 12-17 since the All-Star break.

The Diamondbacks (66-52) are tied with the Colorado Rockies for the NL wild-card lead, but they certainly are not cruising -- despite their 2-0 win over Houston behind Zack Greinke's 6 2/3 shutout innings Monday night.

The D-backs dropped four of six at home last week to the division-leading Los Angeles Dodgers and Chicago Cubs -- with both visiting teams' fans drowning out Arizona's faithful at times -- and they have lost 16 of 29 since the All-Star break. They are 6-6 in August.

That was why beating Houston behind Greinke was so important.

"He's a horse, he's a horse. It's the reason they give him the kind of money they give him," Arizona outfielder J.D. Martinez said of Greinke, who is 8-1 following a Diamondbacks loss this season. "You don't trick people to give you that kind of money ($206 million). He eats up innings and keeps guys off balance, and he never gives in."

Lovullo believes the Diamondbacks' extended slump -- they once were 22 games over .500 -- is partly a byproduct of the calendar and the fatigue that a 162-game season is certain to bring on.

"Early on, it seemed like everything we did was spot on -- we'd make mistakes but we'd find a way to win a ballgame," Lovullo said. "Winning makes the bad go away. A couple of things that have gone on of late is we've made some mental mistakes, (and we) haven't executed in very crucial moments. To me, when you see that for more than two or three games at a time, I would classify that as wandering."

No doubt Lovullo is wondering what kind of performance he will get Tuesday afternoon when rookie left-hander Anthony Banda makes his fourth career start. Banda will oppose Astros right-hander Brad Peacock (10-1, 3.07 ERA). Peacock is 7-1 with a 3.46 ERA in 13 starts and 3-0 as a reliever.

Banda is 1-2 with a 4.60 ERA in his first three starts, losing 8-6 to the Dodgers on Thursday while giving up three runs in four innings. He was better the start before that, limiting the San Francisco Giants to one run over six innings.

In his last outing Thursday, Peacock allowed one run and seven hits in 6 1/3 innings but didn't get the decision in Houston's 3-2 loss at the Chicago White Sox. The start was his second longest of the season; he pitched seven innings against the Seattle Mariners on July 18.

Peacock has won each of his past seven decisions, last losing June 9 to the Los Angeles Angels. However, with ace Dallas Keuchel back in the Houston rotation after a stint on the disabled list, there is a chance he could go back to the bullpen -- at least for the postseason, if not in the coming few weeks.

"When you get to the last six weeks of the season, it's all hands on deck," Astros manager A.J. Hinch said.