"Just call the game. I'm going to follow you. If I need to shake you off, I'm going to shake you off. I want you to do your job," Nova told him.
Then the battery mates went out and led the Pirates to a 3-1 win over the Miami Marlins at PNC Park.
Nova pitched six scoreless innings. Diaz drove in two runs and enjoyed working with Nova.
"It was nice," said Diaz. "He competes all night. He was able to execute every pitch. We got ground balls. We got the outs and we got the win."
Diaz was 2-for-4 with a two-run double in the first, a single hit and a run scored. He is filling in while Francisco Cervelli recovers from a concussion and has reached base in all seven of his starts.
"In my hitting, I try to work every day, stay inside the ball and use the whole field," Diaz said.
Pittsburgh (28-35) earned a split of the four-game series with Miami (27-35) and has won back-to-back games for the first time since May 24-25 at Arizona.
Nova (6-4) was perfect through three innings, including striking out the side in the second. He allowed one hit (a single), struck out four and walked none, and has given up two earned runs or less in six of his 13 starts.
Nova also has pitched at least six innings in all 13 of his starts this season. The last Pirates pitcher to last at least six innings in each of his first 13 starts was Eddie Solomon, who did it in all 17 starts in 1981.
Sunday, Nova got pulled for a pinch hitter, but not because of his performance. Pittsburgh had just taken a 3-0 lead, chased Miami starter Jeff Locke and wanted to sustain the rally.
"It was a run thing," manager Clint Hurdle said. "Bases loaded, one out. Trying to blow it open. That part of it didn't work."
Nova said it also was not a matter of health. He left his previous start with left knee inflammation.
"I wanted to keep going, but there was a situation where we had guys on base and we wanted to extend that lead," he said.
Felipe Rivero pitched 1 1/3 innings for his second save.
Locke (0-2), making his return to PNC Park, allowed three runs and eight hits in 5 1/3 innings with three strikeouts and one walk.
"I did some good things. Did some bad things," Locke said. "But didn't do enough, at the end of the day, to win."
Locke started in the Pirates' organization, where he spent eight years and was an All-Star in 2013 before he was designated for assignment last winter after struggling in 2016 to the point where he was demoted to the bullpen. He signed with Miami as a free agent.
He denied any extra emotion, though.
"Just another game, really," Locke said. "It was a nice day. It was warm. Body felt good. Same thing. No extra motivation. No extra adrenaline. Nothing. Just the same game."
And not an awful one, according to manager Don Mattingly.
"I thought he was OK," Mattingly said. "It ends up being three runs, but I think another solid outing that keeps us in the game if we're scoring any runs."
Pittsburgh opened a 2-0 lead in the first. With two outs, Jose Osuna and David Freese hit back-to-back singles. Diaz drove them in with a double to left-center field.
Miami's J.T. Riddle led off the fourth with a single to left, the first hit off Nova, and moved to second an out later on Freese's fielding error at third. But Nova got out of it on a shallow fly ball and a liner to Freese.
Locke, meanwhile, pitched two perfect innings after the two-run first before Andrew McCutchen smacked a two-out triple to center in the fourth. McCutchen was stranded when Locke got Josh Bell to ground out.
Pittsburgh threatened again with two outs in the fifth. Adam Frazier singled and stole second before Bell walked. They executed a double steal, but Locke struck out Osuna.
The Pirates made it 3-0 in the sixth. They loaded the bases and chased Locke with three singles before Jordy Mercer greeted reliever Brad Ziegler with an RBI base hit.
NOTES: Miami RF Giancarlo Stanton was out of the lineup after leaving Saturday's game with an apparent bruised right wrist, but he struck out in a pinch-hitting appearance. ... Miami 2B Dee Gordon was given the day off from the starting lineup but singled as a pinch-hitter in the eighth and remained in the game. ... With Pittsburgh RHP Jameson Taillon expected to come off the DL and start Monday against Colorado, the Pirates' starters for the rest of the Rockies series are slated to be Gerrit Cole on Tuesday and Chad Kuhl on Wednesday.