SAN FRANCISCO (AP) -- The home runs were upsetting enough but what led up to them concerned Arizona manager Kirk Gibson.
"You look at the first six innings and we made a lot of mistakes," Gibson said after the Diamondbacks dropped an 8-4 decision to the San Francisco Giants on Sunday. "We made a couple of baserunning mistakes, we hit a guy, we walk a guy, we make an error. We weren't able to overcome that."
Vidal Nuno, making his second start for the Diamondbacks, breezed through four innings before running into trouble in the fifth.
Madison Bumgarner became the first pitcher in 48 years to hit two grand slams in a season, and Buster Posey also hit a slam.
Posey and Bumgarner became the first batterymates in major league history to hit grand slams in the same game.
"Even Posey's home run, we had a chance down 4-1," Gibson said. "Then we get into that sixth inning and we didn't have very good inning. It blew up on us."
A double by Bumgarner helped set up Posey's slam in the fifth. Bumgarner homered the next inning - he also hit a slam on April 11 against Colorado.
"Posey's a pitch middle down and he did what he does," Arizona catcher Tuffy Gosewisch said.
Gosewisch came out to talk to Matt Stites about how they were going to pitch to Bumgarner.
"Everybody knows he's a good hitter," Gosewisch said. "I wanted to go first pitch fastball down and away and it just ran back over the plate. I was going to come back with a slider. He was looking for a fastball and he just did a good job of it."
The last pitcher to launch two slams in a season was Tony Cloninger, who hit both in the same game for Atlanta on July 3, 1966, against the Giants at Candlestick Park.
Nuno (0-1) allowed four runs and six hits in five innings during his second start with Arizona.
Cody Ross hit a two-run homer for the Diamondbacks, who are 5-8 in their past 13 games. Martin Prado had three hits and drove in a run. Nick Evans added a pinch-hit RBI double.
Nuno, acquired from the New York Yankees in a trade for Brandon McCarthy, had not allowed a run in his first 11 innings with the Diamondbacks before Posey's slam.
Ender Inciarte and Prado each singled to open the game but Giants outfielder Hunter Pence threw out Inciarte at third base.
"What he saw was Pence bobbling the ball," Gibson said. "What he didn't see was it fell into his hand. That ball hits the grass and he's safe."
Inciarte and Prado again singled to start the sixth inning. With Paul Goldschmidt batting, Bumgarner caught Inciarte taking off early for third for the first out.
"Two strikes, down by three, that was just a mistake," Gibson said.
A double, an infield fielding error and a walk set up Bumgarner's slam in the sixth against Stites. Bumgarner earlier victimized Jorge De La Rosa of the Rockies.
"We had a good conversation about how we were going to attack Bumgarner," Stites said. "I just missed my spot. He's been swinging it well all year."
NOTES: Goldschmidt went 0 for 4 and had his career best streak of safely reaching base end at 32 games. ... Arizona manager Kirk Gibson said he was going to spend part of the All-Star Break watching his son play in the Cape Cod League. ... Ross' homer gave him 501 RBIs for his career.