Iowa meets Maryland in the second semifinal, and the winners will play for the NIT championship on April 4.
"We are playing some of our best basketball right now, and that's going to take us into the [NIT] Final Four," said BYU coach Dave Rose.
Wednesday, two nights after crushing Mercer 90-71 at the Marriott Center, the Cougars showed no signs of travel fatigue, and thoroughly dominated the Golden Eagles, shooting 44.6 percent from the field and 40.7 percent from 3-point range (11 of 27).
"We are playing free and loose and having fun," said point guard Matt Carlino. "Everything is flowing."
After seizing control early in the game with an 11-0 run to answer USM's 5-0 start, the Cougars scored the last eight points of the first half to take a 40-29 lead into the break. They answered every USM surge with a back-breaking 3-pointer or fastbreak layup, playing on attack in the face of the home team's pressure defense.
The catalyst was unsung senior Brock Zylstra, who made five 3-pointers in the first half and finished with 23 points and 10 rebounds for the first double-double of his career.
"It was beautiful," Carlino said of Zylstra's big game.
Tyler Haws added 25 points on 11-for-22 shooting, and Carlino chipped in 15 points, making four 3-pointers, several of which were 4 or 5 feet beyond the arc. Brandon Davies had an off shooting night (5 for 13), but still managed 12 points and 11 rebounds.
It was USM's second home loss of the season, the only other one coming at the hands of Conference USA champion Memphis.
The Cougars assisted on 24 of their 29 field goals
"It is almost a second wind at this point in the year," Carlino said. "We are just not worried. We know what we are capable of, and we showed that tonight."
The three NIT wins mark a remarkable turnaround for the Cougars, who had their streak of six straight appearances in the NCAA Tournament snapped when they lost 72-69 to San Diego in the quarterfinals of the West Coast Conference tournament back on March 8.
"I couldn't be more proud of my guys," Rose said.
BYU 79, Southern Miss 62
O In Short • In perhaps their best performance of the season, the Cougars punch their ticket to the NIT semifinals in New York City with a huge road win at Southern Miss.
Key Moment • Trailing 5-0 a minute into the game, the Cougars put together an 11-0 run and never trail again.
Key Stat • Brock Zylstra makes five 3-pointers, and scores a season-high 23 points for the Cougars.
O BYU vs. Baylor
Tuesday, 5 p.m.
Where • Madison Square Garden, New York