LEXINGTON, Ky. -- Butler relented from its trademarked tight defense in the second half, but the Bulldogs took off the kid gloves and finished strong for a 68-56 victory Bucknell in the NCAA Tournament's East Regional in Lexington, Ky.
The Bulldogs (27-8), seeded sixth, allowed Bucknell to make a 17-2 run and take a 37-33 lead midway through the second half, but Butler answered with two quick 3-pointers to retake a lead, 39-37.
Those deep bombs, and the second was Rotnei Clarke's shot from NBA range, were unusual because they were the Bulldogs' 3-point baskets of the game, as Butler missed its first 13 tries from behind the arc.
"It may not have been aesthetic the entire game, you know, missing our first 13 3s, but our defense was really good in the first half," Butler coach Brad Stephens said.
The Bison (28-6), seeded 11th, stayed in the game, but Butler's 10-0 run gave the Bulldogs a 53-42 lead with 2:19 to play.
Clarke finished with 17 points to lead Butler. In his last game at Rupp Arena, as a member of the Arkansas Razorbacks, he had a cold shooting night in a 101-70 loss to Kentucky on Jan. 23, 2010.
Clarke was able to make up for his cold first half in his first NCAA tournament game since transferring from Arkansas.
"To see a couple go down in the second half was a good feeling," Clarke said. "It's all about my teammates and about the coaches. They just keep telling me to shoot it, and it's good to have encouragement like that."
Bucknell big man Mike Muscala finished with nine points and 10 rebounds, but Bucknell's chance to upset the Bulldogs required either a big game from Muscala or a breakout performance from one of his teammates.
As the second half unfolded, it became evident Joe Willman was that teammate. He had 20 points, but the rest of the Bison were a combined 13-of-46 from the field against a stingy Butler defense that took the Bulldogs to national runner-up finishes in 2010 and 2011.
Muscala, who averaged 19 points and 11 rebounds per game during the season, had two points at halftime on 1-of-9 shooting.
"I think I tried to be aggressive," Muscala said. "I thought I got some pretty decent looks, but (Butler) did a really good job of being physical with me."
Butler's performance against Muscala was no fluke. Butler confused and frustrated Muscala with three different defenders during the first half, flashing different looks without allowing him to find a rhythm.
That was a different strategy than what Butler did against the best center it had faced to date, Cody Zeller of Indiana.
When the Bulldogs beat then-No. 1 Indiana, 88-86, in overtime on Dec. 15, Zeller scored 18 points but was held to five rebounds. Andrew Smith of Butler drew the primary assignment on Zeller that day.
But Thursday, Stephens opted to go with mostly Khyle Marshall and Kameron Woods on Muscala in the first half. He began mixing in Smith late in the half.
Smith finished with 16 points and 16 rebounds.
The Bulldogs forced Bucknell into a hole early in the first half. The Bison were stretched into deep shot-clock possessions and took late, rushed, contested shots.
Bucknell went into halftime shooting 7-of-27 from the field, 0-for-2 from 3-point range and without a free-throw attempt.
"It truly is, truly is a Butler team," Stephens said, comparing his defense to his two national runners-up. "Which I feel really good about, and I think that never showed itself more true than after we got blasted at VCU and came back and won at UMass (to end the regular season).
"That was kind of a telltale moment for me that this is a pretty darn good basketball team."
NOTES: Butler won in its first NCAA tournament game since 2011, when it lost the national championship game to Connecticut, 53-41. The Bulldogs missed the field of 68 in 2012 with a 20-14 record. ... Butler has won its first NCAA tournament game in six of its last seven tournament appearances. The one round-of-64 loss during that span was a 2009 loss to LSU, 75-71. ... Bucknell has not won in NCAA tournament play since its 59-55 victory over Arkansas in the first round of the 2006 tournament. Bucknell was a No. 9 seed that season, still the lowest to date for a team from the Patriot League. ... Bucknell coach Dave Paulsen finished his fifth season as the Bison's coach with 99 career victories. The team's 28 wins in 2012-13 set a record for most by a Patriot League team in one season.