So when Mesoraco came to the plate to face his former teammate with the bases loaded and no outs in the second inning, he wasn't surprised to see that slow curve coming -- and the Cincinnati catcher hit into the seats in left field.
The grand slam gave the Reds the lead for good and they went on to beat Arroyo and the Arizona Diamondbacks 6-4 on Friday night.
"I was aware that he likes to flip that easy breaking ball in there for a first-pitch strike, especially in situations where he really needs a strike," Mesoraco said. "I wouldn't say that I was looking for it, but I went up there with an idea that may be coming."
When Arroyo came to the plate later in the game, he talked to Mesoraco about it.
"I said, `Rac, you were supposed to take one," Arroyo said. `He said, `I couldn't let that one go by."
Mesoraco also had a solo shot off reliever Evan Marshall in the ninth inning for the second two-homer game of his career.
A.J. Pollock doubled twice, singled and scored two runs for the Diamondbacks. In the first five games of the homestand, Pollock is 11 for 20 with five doubles, a triple and a home run and has scored nine runs.
Mike Leake (3-4) gave up four runs, three earned, and six hits in six innings for his first win in eight starts. He struck out four and walked one.
Arroyo (4-4), facing his former team for the first time, allowed five runs and nine hits through seven innings.
"Regardless of the results, that was one of the more enjoyable games I have pitched," he said. `When you know someone that intimately, it is nice to know that the guys are beating you that they are good guys and it was a fun competition."
Mesoraco's second career slam came on the first pitch after the Reds opened the second inning with three consecutive singles.
Aroldis Chapman pitched a perfect ninth for his sixth save.
Roger Bernadina doubled in Cincinnati's other run.
Arizona got two runs in the third. With two outs, Pollock lined one past Frazier at third base. It was originally ruled an error but later changed to a double. Gerardo Parra followed with an RBI single. He took second on the throw home, then scored when Frazier fielded Paul Goldschmidt's slow bouncer and threw it high over the head of Bernadina at first and into the Reds' dugout.
Arizona squandered a chance to tie it in the fifth. Ender Inciarte led off with a double down the right field line and took second on Arroyo's sacrifice bunt. But Pollock bounced to the pitcher and Parra grounded out to shortstop to end the threat.
The Reds got a run in the sixth on Bernadina's RBI double, and Arizona answered with one in its half of the inning. Aaron Hill singled home Goldschmidt from second, leaving runners at first and third with one out.
Chris Owings struck out, then Inciarte was called out at first with Leake taking the throw from second baseman Brandon Phillips and covering on a close play. Manager Kirk Gibson challenged the call but it was upheld on review. The tying run would have scored had the challenge been successful.
"That was a huge play right there," Cincinnati manager Bryan Price said. "I wouldn't say a game-saver, but maybe a game-changer for sure."
The Reds' Billy Hamilton stole his 19th base of the season. ... When Miguel Montero threw out Bernadina trying to steal third in the sixth, it was just the third caught stealing for the Arizona catcher in 28 tries. ... In the third game of the series Saturday night, the Reds have Johnny Cueto (4-4, 1.83 ERA) on the mound against Arizona's Brandon McCarthy (1-6, 4.87). ... Cincinnati is 26-11 with the roof closed at Chase Field, 5-12 with it open. It was open Friday night.