BATON ROUGE, La. (AP) — Matt Clark was barely out of the batter’s box when his screaming liner to right field cleared the wall and bashed against a purple and gold billboard boasting LSU’s five national championships.

There was perhaps no better way for Clark to make a case that this year’s Tigers squad believes 2008 could be the next year on that list.

‘‘Nothing’s better than hitting a ball off the national championship sign,’’ Clark said. ‘‘It kind of just rings and everybody sees where you hit it and you look up and there’s five national championships there. If we keep playing like we are, maybe it will give us a chance’’ to win another.

Clark blasted his 24th and 25th home runs of the season, both two-run shots, and LSU ran the nation’s best winning streak to 22 with a 13-4 triumph over Southern Mississippi in the Baton Rouge regional on Saturday night.

Skip Bertman, who coached LSU’s five national championship teams and is set to retire as athletic director in a month, missed the game after being hospitalized with what doctors described as the early signs of a heart attack. LSU spokesman Herb Vincent announced immediately after the game that Bertman was resting comfortably in a hospital after a successful procedure to place a stent in a main artery.

Certainly, Bertman will want to see the highlights.

Blake Dean, Michael Hollander and pinch hitter Ryan Ochinko also homered for LSU (45-16-1), which hasn’t lost since falling to Georgia on April 19. It is now tied with the 2000 South Carolina squad for the longest winning streak by a Southeastern Conference team in the SEC’s 75-year history.

Dean’s homer was his 19th of the season, his third in two days and seventh in eight games.

Clark also has three home runs in LSU’s first two games of the NCAA tournament, and he and Dean have gone deep in the same inning once in each game. Dean also hit a towering RBI double to the wall in dead center field.

‘‘It’s awesome when everybody in the order is swinging,’’ Clark said. ‘‘They’re all not like lazy fly balls and the wind’s not taking them. Those balls are hit on a line outta here, so that lets you know that one through nine is hitting the ball well.’’

Southern Miss (41-21) now must play New Orleans on Sunday afternoon, with the winner of that game playing again that night against a sizzling LSU squad that has plated 25 runs in its last two games combined.

LSU starter Ryan Verdugo (9-2) lasted five innings for the win, giving up four runs on six hits while striking out four. Tigers reliever Louis Coleman entered the game with LSU leading 8-4 in the bottom of the sixth and pitched three shutout innings of relief while the Tigers pulled away.

Southern Miss starter Todd McInnis (6-3) took the loss.

McInnis struck out four batters and didn’t allow a base runner through the first two innings.

However, he opened the top of the third by walking DJ LeMahieu, who took third on Leon Landry’s single and scored when Ryan Schimpf grounded into a double play.

That was all LSU got in the third, but McInnis came unglued in the fourth after giving up a solo home run to Dean that sailed far beyond the right-center field wall to make it 2-0. McInnis then walked Derek Helenihi before Clark’s sizzling homer to right, which hit a billboard commemorating LSU’s five national championships, made it 4-0.

LSU wasn’t done. LeMahieu followed Clark with a sharp single to center, then came around to make it 5-0 when Leon Landry ripped a double down the right field line. Landry was thrown out trying for a triple, ending the inning.

‘‘There were three good innings, but then it just snowballed,’’ Southern Miss head coach Corky Palmer said. ‘‘They outplayed us. They outpitched us and outhit us.’’

James Ewing scored Southern Miss’ first run in the bottom of the fourth after hitting a leadoff double and advancing on consecutive groundouts.

LSU got that run back on Dean’s RBI double.

Then Southern Miss pulled to 6-4 with three runs in the bottom of the fifth, starting when Chris Matesich hit a leadoff double and came home on Michael Ewing’s single. Three batters later, Ewing’s brother James hit a two-out bouncer up the middle that was just out of Verdugo’s reach and drove in two runs.

But Clark’s second homer in the top of the sixth made it 8-4, and LSU made it 10-4 on Schimpf’s two-run double in the top of the eighth.

LSU coach Paul Mainieri gushed about his team’s pitching, defense and hitting, saying the victory might have been one of Tigers’ best games all season. He only hopes LSU doesn’t rest on its latest effort.

‘‘I told our players after the game, as great a game as it was we have not won anything yet,’’ Mainieri said.

Bertman, undoubtedly, would concur.