The Fighting Illini used three-point shots to start a barrage, beating Gonzaga, 73-61.

It doesn’t happen often for Mike Tisdale.

But when No. 20 Illinois needs the 7-foot-1 center to hit a big shot, Tisdale will step way back and nail it.

Saturday at KeyArena, it was two three-pointers by Tisdale in the second half that sucked the air out of Gonzaga’s repeated runs during the eighth annual Battle in Seattle.

The Fighting Illini used the shots to start a barrage, winning 73-61 before 14,789 spectators.

Tisdale and reserve guard D.J. Richardson led Illinois (8-1) with 15 points apiece.

“We’re thinking, ‘What’s going on?’ ” Gonzaga senior Steven Gray said about the Illini’s impressive run. “We had to figure out where it was coming from and make an adjustment, which we failed to do. It’s something we’ve got to clean up and start talking because that’s what’s killed us in our losses — these stretches of mental lapses that give other teams good looks.”

Illinois used high screens to pop open for its three-pointers. Tisdale hit two from the same spot at the top of the arc. He was 3 for 5 from long range after entering the game hitting 10 of 30 three-pointers in his career.

Tisdale pumped his fist and roared at his team’s bench as his second three-pointer with 15:14 left helped spark a 14-2 run for a 59-41 advantage Gonzaga couldn’t overcome. The Fighting Illini made four three-pointers during the span and was 12 for 23 from beyond the arc.

Each of Tisdale’s treys forced Zags (4-3) coach Mark Few to call time out. Only the coach didn’t have many answers against Illinois’ defensive pressure, and Gonzaga’s aggressive defense was useless with the Fighting Illini sinking NBA threes like layups.

“That was the game,” Few said. “We just were not executing what we had been working on to cover the ball screen. It was a double high ball screen, which you really don’t see that with a (center) popping out.”

The Zags went on a 10-0 run to close to 67-57 with five minutes left following a pair of free throws by Gray.

But the Zags couldn’t get their own three-point attempts to drop, hitting just two field goals to close.

It’s the third time in less than a month Gonzaga has played a ranked opponent. And the Zags’ supersized nonconference schedule is taking a bite out of their confidence. The Zags lost to No. 5 Kansas State 81-64 and No. 17 San Diego State 79-76 in November.

“It’s frustrating, but we have to learn from it,” said Gonzaga’s Robert Sacre, who led his team with 15 points and 10 rebounds. “We can’t make it a habit, and with these guys, we don’t like bad habits. We’re going to try to change from it.”

Illinois’ victory avenges an overtime defeat against Gonzaga last season in Chicago. Coach Bruce Weber said he used clips of the game as motivation for his players, who were relaxed on their coverage of Gray last season.

Saturday, Gray was closely tailed by Richardson and finished 3-for-12 shooting for 10 points and three assists.

“We never let him get in a rhythm,” Weber said of Gray. “I know we made shots, but the key for me was we guarded the heck out of them.”

Forward Elias Harris returned to Gonzaga’s lineup after suffering a right Achilles strain. He finished with 12 points and five rebounds on 6-for-12 shooting.

“It’s a little bit sore now,” Harris said of the injury. “That (the three-pointers) broke our neck at the end. That’s what lost us the game, just a five-minute streak of them shooting three-pointers like crazy.”

Jayda Evans: 206-464-2067 or jevans@seattletimes.com

ILLINOIS (8-1) — Richardson 6-12 1-2 15, Paul 3-5 4-4 12, Davis 5-10 0-0 10, McCamey 3-9 2-3 11, Tisdale 3-7 6-7 15, Leonard 0-0 0-0 0, Richmond 1-5 0-0 2, Cole 3-5 0-0 8, Griffey 0-1 0-0 0. Totals 24-54 13-16 73.

GONZAGA (4-3) — Sacre 5-10 5-6 15, Goodson 4-7 0-2 8, Arop 3-6 0-0 7, Olynyk 2-5 2-2 7, Gray 3-12 3-4 10, Carter 0-1 0-0 0, Stockton 0-0 0-0 0, Harris 6-12 0-2 12, Monninghoff 0-4 0-0 0, Dower 1-2 0-0 2. Totals 24-59 10-16 61.

Halftime — Illinois 34-28. Three-point goals — Illinois 12-23 (Tisdale 3-5, McCamey 3-5, Paul 2-3, Cole 2-4, Richardson 2-5, Richmond 0-1), Gonzaga 3-16 (Olynyk 1-2, Arop 1-3, Gray 1-4, Carter 0-1, Monninghoff 0-3, Harris 0-3). Fouled out — None. Rebounds — Illinois 27 (Davis 6), Gonzaga 40 (Sacre 10). Assists — Illinois 14 (McCamey 7), Gonzaga 12 (Goodson 4). Total fouls — Illinois 17, Gonzaga 19. A — 14,789.