The third-seeded Cougars improved to 23-11 while playing incredibly well on offense for the second straight game, and moved into an NIT quarterfinal game against No. 1 seed Southern Mississippi.
The Eagles (27-9) downed Louisiana Tech 63-52 on Monday, and will host the Cougars at 6 p.m. MDT Wednesday in Hattiesburg, Miss., because they are the higher-seeded team.
The winner of Wednesday's game, which will be televised by ESPNU, advances to the NIT Final Four in New York City.
With the way the Cougars have played since losing 72-69 to San Diego in the quarterfinals of the West Coast Conference tournament, they can't be counted out.
"I thought tonight that we were really good," Rose said. "... The slogan we are rolling on is simple: 'go out and get another game.' ... The disappointment of the conference tournament was real to our players. They really feel excited about this opportunity to keep playing."
Playing like he knew it was going to be the final home game of his storied career, senior Brandon Davies carried the Cougars from almost the opening tip, finishing with 26 points and 10 rebounds.
"We just couldn't keep it out of Davies' hands," said Mercer coach Bob Hoffman. "He's a talented guy."
Davies got plenty of help, as he did in the Cougars' 90-79 win over Washington last week. Tyler Haws chipped in 24 points, while Matt Carlino had 18 and Brock Zylstra 14 in his final home game.
"When we find that third scorer, we have been pretty good all season long," Rose said. "Tonight, we got four."
Mercer's Travis Smith (19 points) hit a 3-pointer to open the scoring, but that was the only lead the visitors from Macon, Ga., would get. Carlino hit a 3, Zylstra hit a 3, and then Carlino followed with a 3, and before Mercer could catch its breath, it was 11-3 just two minutes into the game.
BYU built a 17-point lead in the first half, but Mercer cut it to four and trailed just 44-35 at the break.
The Eagles made another nice run in the second half to trim the deficit to four once and five another time, but more BYU 3-pointers stemmed the rallies.
"It was a shootout, and we didn't make enough shots," Hoffman said. "... I would like to measure a few of those [deep] 3-pointers that Carlino made."
The Cougars were 10 of 24 from 3-point range, while shooting 46 percent from the field. Mercer was 9 of 22 from beyond the arc, but got outrebounded 43-31 and gave up 20 points off 12 turnovers.
Storylines BYU 90, Mercer 71
R BYU's Big Three rolls again, and the Cougars take an easy win over Mercer in an NIT second-round game.
• Brandon Davies tallies 26 points and 10 rebounds in his final game at the Marriott Center.