Josh Donaldson doubled, tripled and drove in two runs for the A's, who had dropped five of seven before knocking around Giants starter Tim Hudson.
Reddick's third home run this spring came on the first pitch he saw in the sixth and ricocheted off one of the flag poles behind the seats in right field. A Gold Glove winner in 2012, Reddick also made a nice play to chase down Pablo Sandoval's deep fly to right-center in the sixth.
''It seems like the swing is coming into play the last week and a half,'' Reddick said. ''That's just what I want going into the season.''
Hudson was touched up for the third time in his last four outings, allowing four runs and six hits over six innings. Five days after a stellar start against the Chicago White Sox, the right-hander walked one and struck out six.
Athletics: Kazmir threw 78 pitches in 5 1-3 innings and spent much of his night working on his off-speed repertoire. What really taxed the Oakland left-hander, however, were his two at-bats against Hudson. Kazmir drew a walk in the third and laid down a sacrifice bunt in the fifth.
''It might not look like I did much, but that took a lot out of me,'' said Kazmir, who was batting for the first time this spring. ''Just having those takes and doing a little hip turn made me tired pretty much all those four pitches. I don't think I'll do that again. I'll probably just stand there (like a) statue to maybe save a little bit of energy.''
Giants: Hudson wasn't nearly as sharp as he was against the White Sox. He pitched with runners on base in every inning except the first.
''I wasn't able to finish some guys off when I needed to,'' Hudson said. ''I'm still a little ways away. I feel I'm close enough to go out there and compete and give us a really good chance to win.''
Athletics: Second baseman Nick Punto was held out with a hamstring injury, but manager Bob Melvin hopes to have the veteran infielder in the lineup Friday. Punto, who signed a one-year deal in the offseason, will platoon at second with Eric Sogard.
Giants: Sandoval went hitless in four at-bats in his return to the lineup after cutting his right hand while running the bases earlier in the week. Just having Sandoval back is encouraging because his primary backup at third base, Joaquin Arias, will be getting the majority of work at second until injured Marco Scutaro returns.
Scutaro will start the season on the disabled list because of lingering back issues. He is scheduled to field grounders and do some light hitting before Friday's game.
Scutaro's absence has left a hole in the No. 2 spot of San Francisco's lineup, and manager Bruce Bochy plans to use Hunter Pence in that slot for the time being.
''He does give you speed, plus he's a guy who can hit the ball out of the ballpark, too,'' Bochy said of Pence, who went 2 for 4. ''That's not a bad thing to have at the top of the order.''
Apparently someone forgot to tell the scoreboard operator at AT&T Park about Bochy's plan.
When the starting lineups were put on the main scoreboard in center field, Pence's name was listed seventh while Brandon Hicks was at second base and No. 2. The problem was that Hicks wasn't even in the lineup - Arias started at second - and Pence was five spots lower in the order than Bochy wanted.
LEFT FIELD BLUES
New Giants left fielder Mike Morse had a rough time in his first home game at AT&T Park.
Morse took a bad angle and nearly overran Donaldson's RBI double down the third base line in the third inning, then dropped Reddick's two-out fly in the fourth. Morse later came up short when he tried to make a diving catch on Donaldson's sinking liner in the fifth that turned into a triple.
CESPEDES WARMING UP
Oakland outfielder Yoenis Cespedes left the Cactus League batting just .154 but looked much more comfortable at the plate back in Northern California. The Cuban slugger doubled down the third base line in his first at-bat, hit into a 5-4-3 double play and then singled and scored on Reddick's home run in the sixth. He also struck out swinging in the eighth.