2002 Oakland Athletics: 20
The mother of all modern winning streaks was produced by Oakland’s third straight postseason-bound, shoestring-budget team. After winning 91 games and the AL West in 2000 and 102 games and the wild card in '01, the '02 A's were 68-51, sitting third in both the division (4 1/2 games behind the Mariners) and the wild card race (2 1/2 games behind the Angels), before beating the Blue Jays in Oakland on Aug. 13. That year's AL Cy Young winner, Barry Zito, pitched eight innings of four-hit ball in the 5-4 win while Jermaine Dye clubbed a three-run homer early and Eric Chavez broke a 3-3 tie with a two-run single in the bottom of the seventh.
The A's took the series finale the next day, swept three games from the White Sox at home and then ran through a three-city 10-game road trip without a loss. They returned home having won 15 in a row and eventually pushed the streak to 20 in a row, the last three coming on walk-off wins: one against the Twins on a walk-off homer by eventual AL MVP Miguel Tejada, and two against the Royals. Win No. 20, which set an AL record, came on Sept. 4, a game in which Oakland blew an 11-0 lead to a Kansas City team that would lose 100 games that year. With the game tied in the bottom of the ninth, pinch-hitter Scott Hatteberg homered off Jason Grimsley, a moment that provided the centerpiece of Michael Lewis' industry-shaking book Moneyball and the movie of the same name that followed.
By the end of the streak, the A's led the division by three games. They finished with 103 wins and the AL West title, but lost a five-game Division Series to the Twins.