The teams' recent play adds intrigue to the matchup of potential playoff teams this weekend.
The Cubs (59-54) are leading the National League Central, but the streaking St. Louis Cardinals are only one game behind. The D-backs (64-50) are 5 1/2 games ahead of the Cardinals for the second NL wild card, but they have fallen 17 games behind the NL West-leading Los Angeles Dodgers.
The Cubs won 14 of their first 17 games following the break to overtake the Milwaukee Brewers for the division lead, but they are only 2-6 since.
Chicago's worst loss might have been catcher Willson Contreras, who sustained a hamstring injury in a 3-1 loss at San Francisco on Wednesday. He is expected to be out for two to four weeks.
Contreras hit five home runs in six games before leaving the Wednesday game in the eighth inning, and he was second in the majors with 10 homers since the break. Trade-deadline acquisition Alex Avila is expected to handle most of the catching duties while Contreras is sidelined.
The Cubs have lost three series in a row as they send John Lackey (9-9, 4.81 ERA) to face Arizona on Friday. Lackey will oppose Taijuan Walker (6-5, 3.60).
"We came out with a lot of energy, played well post-break, and now we're just getting back into that thing where we have to push ourselves mentally, more than anything, to get over the hump," Cubs manager Joe Maddon said after the double-whammy loss to the Giants on Wednesday. "It's not a lack of guys being mentally involved. They're there. But we've got to somehow almost will ourselves to win."
Arizona is 14-22 since going a season-high 22 games over .500 on June 27. The Diamondbacks took two of three from the Cubs when the clubs met at Wrigley Field from Aug. 1-3. The Cubs won the first game 16-4 before Arizona took 3-0 and 10-8 victories.
Lackey did not pitch in that series, but he has never lost to the Diamondbacks, going 4-0 with a 2.76 ERA in five career starts. He is 6-5 with a 4.83 ERA in 11 road starts this season.
Walker, who will turn 25 on Sunday, has allowed more than three earned runs in only one of his past 13 starts. He will make his first career appearance against the Cubs after missing them in the series earlier this month. He is 4-3 with a 3.11 ERA in 10 starts at Chase Field this season.
Walker began with six scoreless innings Saturday against the Giants in his most recent start. However, he gave up two doubles and a homer to the three batters he faced in the seventh and left with a no-decision in the Diamondbacks' 5-4, 10-inning loss.
"He's had a lot of really good games where he might not have had the greatest results, maybe made a mistake or two that led to him giving up a couple of extra scratch runs," Arizona manager Torey Lovullo said.
"Every time he is out there, he has given you five-plus innings and you look up at the scoreboard and he's got close to 10 strikeouts. That is really nice to feel when you are the manager, knowing you are going to get that on a pretty consistent basis. We're not going to take that for granted. We know he is prepared for every start."
Walker is averaging a career-high 8.4 strikeouts per nine innings.