Third-ranked Gonzaga scored 18 unanswered points between the first and second halves and cruised to their 20th consecutive victory to start the season in an 83-64 win Monday night over host Portland in a West Coast Conference game.

"It hasn't been easy, but it's nice to be 20-0 for sure," said freshman reserve forward Zach Collins, who led the Bulldogs with 13 points and eight rebounds. "We don't try to look ahead or look back. We've done a great job of staying focused on each game."

The Bulldogs (8-0 in the WCC) made 51.7 percent of their shots with six players scoring at least eight points. Guards Silas Melson and Jordan Mathews each had 12 points. Center Przemek Karnowski scored eight points (making all four his field goal attempts) with five rebounds and five assists.

Portland guards Rashad Jackson and D'Marques Tyson led the cold-shooting Pilots (9-11, 2-6) with 15 points apiece. They were a combined 10 of 21 from the field and 7 of 10 from 3-point range while their teammates made only 13 of 43 shots overall.

The matchup was a rescheduled game after the originally slated game at Portland's Chiles Center on Jan. 7 was postponed because of inclement weather that included snow and freezing rain.

Gonzaga, the lone unbeaten team remaining in the nation, defeated Portland 73-52 two days previously in Spokane, Wash.

"It's definitely weird playing back-to-back games like that," Collins said. "I haven't done that, not even in high school.

"It was a good experience because we tried to capitalized on the weaknesses we exposed back home and also work on some of the mistakes we made the first time we played them."

After the previous game, Gonzaga coach Mark Few was critical of the Bulldogs getting out-rebounded 41-33.

The Bulldogs won the rebounding battle 41-36 Monday with forward Johnathan Williams contributing seven. The Bulldogs also had nine fast-break points as opposed to only two in the first meeting.

"This is the No. 3 team in the country and we're down our best player," Portland assistant coach Bob Cantu said, referencing a season-ending knee injury suffered last week by leading scorer Alec Wintering.

"We have so far to go to beat a team like Gonzaga (with Portland playing its first season under coach Terry Porter, a former NBA player and coach). I don't know if Gonzaga will lose. Their next loss might not come until the Final Four or the national title game or they won't lose at all."

Gonzaga took control of the game in the first half Monday behind the play of its reserves. The Bulldogs' bench outscored Portland's reserves 18-2 by halftime, ultimately outscoring the Pilots 40-28 in that category.

Melson, Collins and Killian Tillie combined for the points by the bench in the first half, shooting 4 of 7 from the field while making all eight free throw attempts. Melson made two of three from 3-point range and Collins had six rebounds to lead the Bulldogs to a 38-23 halftime lead.

Portland went scoreless in the final 3:59 of the first half. Gonzaga ended the half with an 8-0 run, the last six points contributed by Tillie, Collins and Melson.

Tillie had to be helped off the court in the second half with an ankle injury. The severity of the injury and his playing status for Thursday's home game against San Diego was not announced after the game.

Gonzaga scored 10 points in the first two minutes of the second half to pull away further on two baskets by Karnowski and a 3-pointer each by Josh Perkins and Mathews. The 18-0 run between the first and second half built the Bulldogs' lead to 48-23. Gonzaga led by as many as 33 points in the second half.

NOTES: Gonzaga G Nigel Williams-Goss, who left Saturday's game early with a sore back, played 26 minutes Monday night. He scored four points on 2 of 9 shooting from the field. ... With Portland leading scorer Alec Wintering out for the rest of the season with a knee injury, the Pilots will rely on freshman PG Andre Ferguson, who played a season-high 23 points at Gonzaga last Saturday in their first game without Wintering. Ferguson played only 54 minutes all season before that game. ... Gonzaga's 19-game winning streak to start season is the fourth-longest in program history, just one win behind runs in 2005-06 and 2003-04. The 2014-15 Zags won a program-record 22 straight games. ... The last time Gonzaga played the same opponent back-to-back was in 2008, when Gonzaga beat Santa Clara in the regular season finale, before defeating them again the opening round of the West Coast Conference Tournament. ... Portland coach Terry Porter has used different starting lineups in each of the last five games before Monday night due to various injuries and trying to find the right combination.