The Tigers (11-6) entered their final at-bat down 2-0 following an excellent performance by Eagles' senior left-hander pitcher Jeremy Plexico, who was in the midst of a 3-hit shutout performance.
"He gave me a fastball inside on the first pitch and I fouled it off," said Harris. "He gave me the same pitch again and I got a good swing on it."
Ivan Naccarata followed with a double into the right-center field gap, and the Eagles replaced Plexico with freshman right-hander Kevin Slowey. LSU head coach Smoke Laval countered by pinch-hitting Blake Gill for Jon Zeringue.
Gill was intentionally walked and Lavall then decided to pinch-hit J.C. Holt for Greg Smith. Holt drew a walk to load the bases, and catcher Matt Liuzza was hit by a pitch to bring in the winning run.
"A win is a win and you take them any way you can get them," said Harris. "But we would have liked to score some runs and put them away earlier."
The LSU bats that had been so thunderous on Friday and Saturday were silenced Sunday by Plexico. After putting up 27 hits in the first two games, the Tigers managed only five in the final game before their ninth-inning rally.
Plexico exercised outstanding control of his fastball. While LSU managed to make a lot of contact, the result was steady stream of pop flies that Winthrop fielders swallowed up.
LSU didn't get a runner into scoring position until the eighth inning.
"For two games, we were hitting doubles and homers and really driving the ball," said Laval. "Today our swings just weren't there. We didn't drive the ball like we're capable of doing."
Winthrop (9-6) took their first lead of the series in the fourth inning when third baseman David Scoggin brought in Grant Neidenfeuhr with a bases-loaded ground ball to shortstop.
In the fifth inning, second baseman Matt Matkovich brought in Matt Repec with a single in the right-center field gap.
LSU starting pitcher Jake Tompkins, who had struggled with the velocity on his pitches in previous starts, was solid in his first Sunday start of the year. He didn't pick up a decision in the game but lasted seven innings, giving up five hits, two runs, striking out seven and walking four.
Redshirt freshman Jason Determann relieved Tompkins in the final two innings and picked up the win, his first of the year.