"There was a lot of adrenaline," Haren said. "Once that first inning was over, the nerves kind of settled in and I was able to just pitch."
Haren pounded the strike zone throwing 63 of his 92 pitches for strikes, and he threw first-pitch strikes to 20 of the 24 batters he faced. In fact, the lone time Haren had three balls on a hitter was in the second when Chase Headley hit a 3-1 fastball for a double.
"I was super aggressive in the strike zone," said Haren, who threw mainly two and four-seam fastballs and some cutters, while only going to his curve and split on occasion.
Haren was able to be aggressive because the D-backs offense gave him a nice cushion to work with, scoring six runs in the first four innings.
Of the six runs, just two were earned, as Arizona capitalized on a pair of San Diego errors. All six of the runs came with two outs in an inning.
"The only way they're going to come back in a game like that is usually a few walks and a big hit, so I wasn't going to walk anybody," Haren said. "You get that lead -- makes things a lot easier."
In the first inning, Miguel Montero drove in a pair with a single. In the third, a two-run homer by Mark Reynolds gave Arizona a 4-0 lead, and finally, Stephen Drew smacked an inside-the-park homer that scored Haren all the way from first base in the fourth.
It was all that running on the homer that came closer to knocking Haren out of the game than the Padres did.
"Oh, I was tired," Haren said. "I didn't catch my breath until the inning after that."
Haren did not walk a batter and fanned four.
"We couldn't get anything going," Padres manager Bud Black said. "We didn't have a lot of good swings."
Montero said it was an easy day for him behind the plate the way Haren was throwing.
"He painted," Montero said. "He was throwing to the corners. It's going to be hard to put the barrel on it because those pitches are perfect."
This was the second career Opening Day start for Haren and his first in an Arizona uniform. He has made three straight All-Star Games and Hinch thinks his ace resides in rarified air.
"I think he's among the best," Hinch said. "There are a lot of good ones out there. His name should be mentioned up there with the likes of Roy Halladay, [CC] Sabathia, [Tim] Lincecum, guys that are perennial award winners."
"I don't need to be mentioned with those guys," Haren said. "I know this team needs me to be good, and if I go out and do what I did today for 33 more times, we'll be alright."
Haren did his best to play down the importance of the Opening Day start beforehand, but he acknowledged afterward that he knew it was key for a team that struggled through a last-place finish in 2009 to avoid another slow start.
"It's nice to get the first win out of the way and just go on from there," he said. "We can't get off to that kind of [slow] start. Getting off to a good start is big and hopefully, just win the series and move on from there. I think small-term goals are better and smarter for us. First winning that game, then the series and taking care of our business at home is also important."