Blalock, a third baseman for the Texas Rangers, hit a two-run homer in the bottom of the eighth off Dodgers closer Eric Gagne to give the American League a 7-6 victory - and a sixth straight All-Star Game win to cut the National League advantage in the series to 40-32-2.
Gagne entered the bottom of the eighth protecting a 6-4 National League lead.
Garrett Anderson, who was named the All-Star Game Most Valuable Player a day after winning the Home Run Derby, doubled with one out to start the game-winning rally. Toronto center fielder Vernon Wells doubled with two out to score Baltimore's Melvin Mora, who had pinch-run for the Angels' left fielder.
Blalock then came up as a pinch-hitter for another San Diego County prep product, Angels' third baseman Troy Glaus (Carlsbad High). Blalock homered to right center, scoring Wells ahead of him.
The game started as a pitching duel and again a local high school product was involved. Rival starters Esteban Loaiza (Mar Vista High) of the Chicago White Sox and Jason Schmidt of the Giants each allowed a hit over two scoreless innings.
The American League got on the board first with a single run in the third off Phillies pitcher Randy Wolf. Seattle right fielder, who received the most votes for a record-tying third straight year, drew a one-out walk, stole second and scored on a two-out single by Toronto first baseman Carlos Delgado.
But the National League took what appeared to be a commanding lead with five runs in the top of the fifth.
Atlanta right fielder drew a walk from Seattle's Shigetoshi Hasegawa to open the inning and scored on a two-run homer by Colorado first baseman Todd Helton to give the National League a 2-1 lead. Cardinals third baseman Scott Rolen followed with a single. Hasegawa retired the next two hitters before pinch-hitter Rafael Furcal of the Braves singled.
Eddie Guardado of the Minnesota Twins replaced Hasegawa and immediately gave up a two-run double to pinch-hitter Andruw Jones of the Atlanta Braves. Jones scored the inning's fifth run on a single by Cardinals' left fielder Albert Pujols.
The American League narrowed the gap to 5-3 in the bottom of the sixth off Woody Williams of St. Louis on a two-run homer by Anderson following a lead-off walk drawn by Rangers' shortstop Alex Rodriguez.
Jones got one of the runs back in the top of the seventh with a solo homer off Oakland's Mark Mulder to make it 6-3. Yankees first baseman Jason Giambi homered off Billy Wagner of the Astros.
That set it up for the American League's three-run rally in the bottom of the eighth.
Rondell White was the Padres' lone representative and grounded into a doubleplay while pinch-hitting for the Giants' Barry Bonds in the seventh.
Anderson paced the American League's nine-hit attack going 3-for-4 with a double and a home run for two RBIs. Jones was 2-for-2 with a double and a homer with three RBIs and two runs scored as the only National Leaguer with more than one hit.
Gagne suffered the loss for the National League. Anaheim's Brendan Donnelly worked a perfect eighth for the American League to get the win. Keith Foulke of Oakland worked a perfect ninth to get the save.