Illinois State (37-22), which had won the Missouri Valley Conference tourney for the first time since 2001, left the bases loaded in the final inning of a 2-1 loss to No. 9 Missouri, which was playing at home in Columbia, Mo.
The Tigers (46-12) advanced to the Super Regional for the fifth straight year - four at home. They meet Louisiana State in a best two-of-three series, from which the winner becomes one of eight teams in the Women's College World Series.
Missouri junior Chelsea Thomas of Pleasantville, Iowa, one of the nation's top pitchers, struck out the side in the ninth inning to preserve Sunday's win, giving her 12 strikeouts for the game. Thomas won all three regional games, allowing just 11 hits and one run while fanning 28 in 22 innings.
It was the ninth time in nine NCAA tournament appearances Illinois State has failed to get past the regionals. The Redbirds, who also lost to Missouri 6-0 Friday, needed to beat the Tigers twice Sunday to advance.
Northwestern (29-29), which had made the tournament by winning nine of its final 10 regular-season games, stayed hot to start the regionals, beating host Texas, the sixth seed, 2-0 in its first game and Houston 13-9 in the second.
The Wildcats, with just one senior regular, went into Sunday's play needing just one more win over Texas in the double-elimination regionals, but it was not to be.
Longhorn junior Blaire Luna, whom Northwestern had beaten Friday, threw shutouts in both Sunday games as Texas rolled to a pair of 5-0 wins. Luna, pitching in her home town, struck out 43 Wildcats in the three games.
Texas (46-11) goes on to play No. 11 Oregon in the Super Regionals.