"I was very excited for this start," said Hahn, traded by San Diego in the Derek Norris deal in the offseason.
The A's right-hander harnessed his emotions and was instead able to let them fuel an impressive 6 2/3-inning outing in which he allowed just one run and three hits in a 9-1 win.
"How I wanted it to go," said Hahn, smiling.
"He was so excited he'd had a good performance," said catcher Stephen Vogt, who drove in five runs to back his pitcher's effort. "A lot of memories for him here. He loved it here, so I think it was a special day for him.
"He's on a pretty good stretch right now. Tonight, he used all four of his pitches really well, kind of the first day I feel like he really put all four of his pitches together. Threw a lot of sliders, a lot of changeups as well, and had the good sinker working."
"I could throw all my pitches for strikes today. I think I was keeping the ball down, able to locate the fastball," said Hahn. "Stephen did a great job of keeping me in it all game. Every inning I came in, he was motivating me."
Hahn has allowed just two earned runs over his last two starts, spanning 13 2/3 innings, and a total of five in his last four outings, lowering his season ERA to 3.62.
"You see a lot more confident pitcher on the mound," said A's manager Bob Melvin. "He's mixing his pitches better, he's ahead of the count, he just looks like he's in command on the mound."
• Left-hander Fernando Abad took a ball off his left ankle in the ninth inning but remained in the game to close out the Padres with a scoreless frame.
• First baseman Ike Davis (left quad) went 1-for-4 with two RBIs in a rehab outing with Triple-A Nashville on Monday. Davis will play another nine innings with the Sounds on Tuesday before being activated Wednesday.