Sooner ace and No. 3 overall draft pick Jonathan Gray dealt nine strikeouts but finally ran into trouble in the eighth inning.
Turns out that eighth inning trouble was all it took for the Tigers to seize a 1-0 series lead.
After falling down 0-2 in the count, second baseman JaCoby Jones ripped a single just past the outstretched arms of OU center fielder Max White in right center and scored a play later on pinch hitter Tyler Moore's double.
So, in the end, despite throwing a solid 7 1/3 innings of two-run ball with five hits and two walks, Gray was the hard-luck loser.
His counterpart Aaron Nola, just a little bit better on this night, picked up the victory while tossing a complete game shutout with six strikeouts and only two base runners, both hits.
OU had its best chance to score in the top of the fifth when first baseman Matt Oberste led off with a double, but a one-out strikeout and groundout stranded him at third.
The loss is the Sooners' first since May 18 and it snaps an eight-game winning streak and perfect 17-0 stretch by OU's diamond clubs after the softball team won their second national championship the other night.
They'll look to even the series and keep their season alive when the two meet again tomorrow at 6 p.m.