Grandal hit a three-run homer to cap a five-run fourth inning and the Padres improved to 34-34 with a 6-4 victory over the Arizona Diamondbacks on Saturday night.
The last time the Padres were at .500 was April 10, 2011 -- when they were 4-4. Their last day above .500 was the finale of the 2010 season, when they finished 90-72.
Marquis (9-2) allowed three runs on three hits in 6 2/3 innings, winning his eighth straight decision to help the Padres extend their win streak to five. San Diego also pulled within three games of first-place Arizona in the NL West.
Huston Street, who came off the disabled list Friday, came on in the ninth and allowed one run but picked up his 12th save in 13 opportunities.
The Padres, who began the season 5-15, have strung together a 29-19 record since April 24th, tied for the second-best mark in the National League in that time. The St. Louis Cardinals have gone 32-16.
"It looks good on paper," manager Bud Black said of the team evening its record. "I think it sends a great message to our guys, it really does. They fought off some hard times in April to where we are now. So I'm very proud of them to get to .500. It's great. I think it proves that we can continue to play solid baseball."
For a while it looked as though the Padres were going to fall short of that elusive .500 goal after the Diamondbacks staked starter Wade Miley to a 3-0 lead through three innings -- thanks in part to a two-run home run by Miguel Montero in the first inning.
Miley faced the minimum over the first three frames and had allowed only a walk to Grandal when Everth Cabrera led off the fourth with a single to right. Chris Denorfia followed with a hard shot to shortstop that Didi Gregorius misplayed for an error.
Chase Headley drove in San Diego's first run with a single to center. After Kyle Blanks reached on a fielder's choice, Logan Forsythe hit a sacrifice fly to score Denorfia. Jesus Guzman followed with a single to right, and Grandal, who served a 50-game suspension for testing positive for elevated levels of testosterone, hit his first homer of the year -- a 442-foot shot into the second deck in left field. That gave the Padres a 5-3 lead on five unearned runs.
"It felt great," said Grandal. "I've been having some good at-bats, squaring some balls up, but obviously the outcome had been different. But it felt so good to get that first home run out of the way."
Grandal thought Marquis did a great job in making adjustments after the first couple of innings.
"I just found myself a little bit mechanically," said Marquis. "I didn't think I was going to get out of the third, but I got a little boost of energy, I felt something in my delivery at the end of the third inning when I was facing the eight and nine hitters and I just rolled with it and things went smoothly from there."
Blanks added his seventh home run in the sixth off Miley with a line shot to left.
"We started out pretty good," said Montero. "Jason (Kubel) seemed pretty upset. But we couldn't get a rally going. Then he made a good pitch (to Miley) to get out of that jam in the top of the fourth. It's frustrating."
Diamondbacks manager Kirk Gibson said he hasn't heard anything about the appeals of his players' suspensions from their fight with the Dodgers earlier this week. Arizona will likely play with a 24-man roster with pitcher Ian Kennedy being given a 10-game suspension. Gibson is confident the suspensions will be staggered, allowing the team to mix and match position players. ... Arizona 2B Aaron Hill was scheduled to make a minor league rehab start Saturday night for Triple -A Reno at Tucson. He will play Sunday, take off on Monday and play for Reno at home on Tuesday and Wednesday. Gibson was hopeful that Hill would play at least five innings. Hill has been sidelined since April 11 with a slight fracture in his left hand. ... Padres OF Carlos Quentin was out of the starting lineup because of an injured left shoulder, which he said he hurt taking a swing on Friday. ... Former Padres catcher John Baker was claimed off waivers by the Los Angeles Dodgers on Saturday and optioned to Triple-A Albuquerque. ... Clayton Richard, originally scheduled to pitch Saturday, will start Sunday. Padres manager Bud Black said he wanted to keep Marquis on regular rest and gave the struggling Richard an extra day between starts. Richard (1-5, 8.06) will be opposed by Kennedy (3-4, 5.49) who is appealing his suspension.