NSU (31-22, 19-9 SLC) moved into a three-way tie for second place with Texas A&M-Corpus Christi and Nicholls. The Demons would have to win both of their final games and have Corpus Christi take at least one from Sam Houston State to claim a share of the league championship.
Northwestern State jumped up 2-0 in the fourth inning, and the Lions (31-23, 16-12) tied the game in the sixth inning. Underwood's triple was part of the Demons' answer with another two runs in the seventh inning.
Nick Heath led off the seventh inning with a four-pitch walk, and took second base on a sacrifice bunt from Joel Atkinson. Garrett Logan followed with a single to left field and advanced to second base when the Lion left fielder attempted to get Heath at home, but the designated hitter remained at third base.
Edwin Gomez hit a bouncer to the right side of a drawn-in infield, but reached on a fielder's choice when Heath was tagged out at home. Underwood took a 2-2 count pitch and lined it down the right field line and scored both runners aboard.
"Good base running by Garrett to take the extra base on the single," said Demon head coach Lane Burroughs. "We've been waiting on someone to get the big hit, and Bret got it tonight. He took a borderline pitch before, and got the call. Sometimes you do, sometimes you don't.
"We ran a down-angle with Nick, and he got thrown out at home. Our guys could've packed it in after that, but don't," said Burroughs. "We got the big two-out triple, and that was huge. I'm proud of Bret and the team for showing some resiliency."
After NSU took the lead, Northwestern State sent in Cameron Brewer to relieve Demon starter Adam Oller. Brewer pitched three innings to finish the game and only allowed one hit and one walk. He took his third save of the year and only faced 11 batters.
"He was very good, and has been now for his last six or seven outings," said Burroughs. "He filled up the zone with all of his pitches. We thought about taking him out for the ninth, but he was throwing so well we let him go back," said Burroughs.
Oller (6-1) earned the win on six innings pitched. He allowed both Southeastern runs on five hits and two walks.
The freshman right-hander got off to a slow start in the first inning. He walked the leadoff man on four pitches, allowed a single to right field from the two-hole hitter and hit the next batter to load the bags with no outs. He struck out the next two batters and induced a ground ball to end the inning without a run.
"The game was kind of in the balance when he loaded the bases," said Burroughs. "He punched out two guys and got the ground ball, which kind of crippled them along with our two runs. I'm very proud of our guys."
Oller sat down eight in a row between the third and fifth innings.
NSU scored its first run of on a single up the middle from Heath that scored Chase Daughdrill, who reached on a single that hit the lip of the grass and jumped over the third baseman. Heath scored when Joel Atkinson put down a bunt that was thrown into the right field bullpen.
SLU scored its runs on a single to right field from Brett Hoffman and a fielder's choice from Daniel Midyett.
Tate Scioneaux (6-6) took the loss on 6.1 innings pitched and three runs allowed (two earned) on six hits and a walk. Jason Greenleaf relieved him and pitched 2.2 innings. He gave up one run on two hits.
Daughdrill was 3-of-4 with one run on the night, and Logan was 2-for-5 with a run scored. Gomez, Underwood and Heath all had one hit on the night. NSU outhit the Lions 8-6, and the Demons left six runners on the bags.
The series finale will be at 2 p.m. today.