BATON ROUGE — The rain never came, but anxious perspiration poured as No. 4 national seed LSU struggled with tempestuous Texas Southern throughout a NCAA Regional opener Friday afternoon before the Tigers finally established order and won comfortably, 15-7, at Alex Box Stadium.

The Tigers (44-17) committed a season high five errors, trailed 2-0 after one, 3-0 in the second and 7-5 in the fifth before finally taking the lead for good at 9-7 in the fifth and finishing with 12 hits, including a pair of home runs by Zach Watson and one by Michael Papierski.

LSU advances to a 7 p.m. game Saturday against the winner of Southeastern Louisiana. Texas Southern (20-33) plays the loser of that game at 2 p.m. Saturday. There is a 60 percent chance of rain of Saturday, though.

"I'm glad that game is over, and I'm glad that we won," a drained LSU coach Paul Mainieri said. "We just didn't play really well. At least we won. It was my fault more than anybody's. I just don't think we looked like a really well coached team out there today, and I'll take the blame for that."

Papierski and Watson struck for back-to-back home runs in the bottom of the seventh inning for a 12-7 lead, and Antoine Duplantis stroked a RBI single for a 13-7 lead. Papierski's home run was a two-run shot to right with Beau Jordan aboard as a hit batsman before Watson's solo shot to left. Cole Freeman then walked and stole second for Duplantis.

Watson previously hammered a three-run home run to left field in the second inning on a pitch at eye level from Texas Southern starter Anthony Martinez for a 4-3 lead. Papierski had just singled in LSU's first run of the game, cutting Texas Southern's lead to 3-1. Watson became the first LSU player to homer twice in a NCAA postseason game since Ryan Schimpf in a 21-7 win over California-Irvine in the Super Regional title game on June 9, 2008, in the last game played in the original Alex Box.

The Tigers added two runs in the eighth for the 15-7 final on an RBI groundout by Jordan Romero and on a wild pitch.

LSU's 15 runs Friday were also the most by the Tigers in the NCAA postseason since that game.

It was a nice finish, but the Tigers looked out of it for most of the game as they booted ball after ball after coming in as the top fielding team in the Southeastern Conference. It was the most errors by LSU in an NCAA postseason game since also committing five in an 8-5 win over Sam Houston State in 2013 when the Tigers reached the College World Series.

Texas Southern knocked LSU starter Jared Poché out of the game in the fifth inning by scoring four unearned runs on two hits, two walks and two errors by shortstop Kramer Robertson for a 7-5 lead. LSU came right back with four runs of its own for the 9-7 lead. Freeman started the rally with a double before an RBI single by Nick Coomes, a sacrifice fly by Jordan, a RBI double by Josh Smith and another sacrifice fly by Papierski.

LSU added a run in the third for a 5-3 lead on a triple by Freeman and a RBI single by Greg Deichmann.

Texas Southern, which finished fourth in the Southwestern Athletic Conference before winning the league tournament to reach the NCAA Regional, took a 3-0 lead over the SEC regular season and tournament champions off Poché, who failed to tie the school career record for wins at 38.

As has often been the case throughout his career, Poché pitched out of trouble in the first inning, but not after Texas Southern made some noise. Kamren Dukes and Jose Camacho led off the game with singles, and Poché walked Gaudencio Lucca to load the bases. After Poché struck out Blake Hicks for the first out, Christian Sanchez singled to deep shortstop, where Robertson fielded and threw to first. But Coomes left the bag and was charged with an error. Dukes scored on the RBI single, and Camacho scored on the error. Poché got Jeremy Thomas to bounce back to the mound, and Poché threw Lucca out at the plate.

Texas Southern looked like it would take a 4-0 lead when Horace LeBlanc III apparently singled up the middle with runners on second and third in the second, but second baseman Freeman fielded the ball deep behind second and made a terrific throw to first to end the inning with no further damage.

LSU went out in order in the bottom of the first against Martinez, who struck out Robertson and Antoine Duplantis swinging, and the Box got quiet.

Texas Southern made it quieter when it took a 3-0 lead in the second inning after two strikeouts by Poché. Dukes reached on a two-base throwing error by Smith at third. Then Camacho singled to center, and the Tigers committed their third error of the game when Watson let the ball slip under his glove in center. Poché got Lucca to ground out to end the inning.

"We were kind of pressing after that," Smith, a freshman like Watson, said. "We were playing the game too fast. Needed to slow down a little more. Getting used to the regional atmosphere may have had a little to do with it."

Poché allowed five hits and seven runs, but only one of them was earned. He walked three and struck out eight. Caleb Gilbert relieved Poché in the fifth and picked up the win to improve to 5-1. He allowed two hits and no runs in two and two-thirds innings with six strikeouts and zero walks. Martinez (4-4) took the loss, allowing eight hits and nine earned runs in four and a third innings with with four walks and three strikeouts.

"I just want our players to forget about this game as quickly as possible and get ready for Saturday night," Mainieri said. "We got away from playing just good, solid baseball."

Glenn Guilbeau covers LSU sports for the USA Today Network of Louisiana. Follow him on Twitter at @LSUBeatTweet.