Then, in the span of three batters the lead was gone as the Tigers used back-to-back homers by Brennan Boesch and Carlos Guillen to beat the D-backs, 3-1, in front of a sellout crowd at Comerica Park.
The loss was Arizona's 15th in its last 16 road games and came one day after it picked up its first win away from home since May 17. The D-backs finished a six-game road trip, which also included a stop in Boston, with a 1-5 record.
"This was very, very, very frustrating to say the least," said Kennedy, whose record fell to 3-5.
Miguel Cabrera led off the seventh with a single to right and with a 1-1 count Kennedy missed his spot with a curveball and Boesch crushed it over the wall in right for a 2-1 Detroit lead.
"I know he's aggressive, but I just thought I could sneak one by," Kennedy said. "It was down the middle, it was supposed to be backdoor and it wasn't."
Kennedy then got ahead of Guillen 1-2 and tried to get him to swing through an elevated fastball as he had in the fourth. Instead, Guillen hit it over the right-field wall.
"It looked like he was looking for that pitch," Kennedy said.
While the three batters do not erase the fact that it was a good outing for him, Kennedy was anything but pleased.
"This is a game where I need to step up," he said. "I mean it's a 1-0 game in the seventh and that's where I need to step up and get a quick inning again."
Tigers manager Jim Leyland, though, was impressed.
"He had good control," Leyland said. "On a hot day he got a couple there he didn't want to and we happened to run into them. But he was tremendous. He really pitched. When you look at him you don't go, 'Oohh and aahh' because you don't see 96 or 97 mph. But this guy is a really good pitcher. I was really impressed. He pitched one of the better games against us that's been pitched this year I felt."
With a two-run lead, the Tigers turned things over to a pair of dominant relievers to close things out.
First there was Joel Zumaya, whose fastball touched 101 mph on the stadium radar gun, in the eighth and then former D-backs reliever Jose Valverde closed things out in the ninth for his 16th save.
"They took the lead at the most opportune time for them with their two big boys at the end," D-backs manager A.J. Hinch said. "They came in and slammed the door. It's pretty simple."
Tigers starter Max Scherzer, who was dealt from Arizona to Detroit over the winter in the same deal that sent Kennedy to the D-backs, was tough on his former mates.
The right-hander was only in real trouble once in the game and that came in the first inning when a two-out double off the left-field wall by Chris Young scored Justin Upton to give the D-backs a 1-0 lead. Scherzer had to throw 36 pitches during the inning, yet he was able to last seven innings as he found a way to be more efficient with his pitches.
"We had him on the ropes early," Hinch said. "He made a nice adjustment and threw more strikes after the first. We know exactly the kind of game he's going to pitch. To his credit he made adjustments and threw a lot more strikes and some finish fastballs and got some big outs."