Going hitless in eight at-bats with runners in scoring position and serving up three homers, the D-backs dropped their third straight game, 6-2, to fall below .500.
"We made it hard on ourselves, that's not who we are," Gibson said. "It's hard to come back and win a game like that. It's disappointing and it was bad baseball. I never like that."
Prior to Monday, the D-backs were 10-2 in their last 12 games at Chase Field, including four straight victories.
Trevor Cahill pitched admirably, but the right-hander committed an error that cost him two runs. At the end of the night, his final line read four runs (two earned) on seven hits over six innings.
"I didn't feel confident in throwing any of my off-speed pitches for strikes," Cahill said. "They were swinging early and I couldn't get my off-speed pitches over for strikes, so I had to go [to the] fastball. With an aggressive team like that, they know what's coming, they are going to hit it."
Cahill's error marked the season-high sixth straight game the D-backs have committed at least one miscue. This coming after the club set a franchise record in June with 114 2/3 consecutive errorless innings.
"That stuff has to stop," Gibson said. "We were on a string where we were playing really good defense, now we've been kicking it around a little bit."
Chris Young and Paul Goldschmidt each drove in a run and accounted for three of the team's eight hits. Aaron Hill, who is eligible for the All-Star Game Final Vote, went 1-for-4 and made a nice play in the field to prevent at least one run from scoring in the third inning.
"Trevor did a good job of keeping us in it," Goldschmidt said. "We just couldn't get that big hit."
Padres starter Clayton Richard kept the D-backs at bay for much of his outing, despite finding himself in trouble frequently. The southpaw scattered eight hits over 8 2/3 innings and surrendered just two runs. The 28-year-old hasn't given up more than three earned runs in a game since June 6.
"You have to give Richards credit, he was throwing the ball good," Gibson said. "You expect to be in a tight game and you hope you can stay with him and not make mistakes on our side of it. When you get opportunities from him, you have to take them."
Alexi Amarista delivered most of the damage for the Padres, collecting three hits and driving in three runs. His first big hit of the night, a solo homer to right field, came in the first inning to put the Padres up 1-0.
The D-backs put a runner on second base in the second, third and fourth innings, but failed to capitalize, going a combined 0-for-5 with runners in scoring position during that stretch.
"We didn't get them over and we didn't get them in," Gibson said. "Just did not execute very good overall. It's something we need to fix."
The Padres put the game out of reach in the top half of the sixth inning, thanks to a Cameron Maybin solo shot and an Amarista two-out, two-run double to make it 4-0.
Maybin's home run traveled an estimated 485 feet, according to ESPN Sports & Info Group, making it the longest homer in the Majors so far this season and fourth-longest by an opponent in Chase Field history.
"I was trying to throw a strike and not walk anybody," Cahill said of the pitch to Maybin. "I threw a splitter and he hit it."
The D-backs had a chance to get out of the sixth inning with just one run against them, but Cahill's error came on a dropped throw at first base from Hill, allowing Everth Cabrera to reach and extending the frame.
"I took my eye off it at the last second to see if I was on the bag," Cahill said. "I just didn't look it all the way in."
The first two batters of the D-backs' half of the sixth reached base, but the next three hitters all swung at the first pitch and recorded outs to end the potential rally.
After Yasmani Grandal hit a solo homer off of Mike Zagurski in the seventh, Young knocked his third home run of the past week to cap the D-backs' scoring.