LAS VEGAS (Interstat) — Alyssa Thomas scored 20 points and the Phoenix Mercury walloped the Las Vegas Aces 99-66, making sure the only celebration for the reigning WNBA champions on Saturday would be their pregame ring ceremony.

The win was a measure of revenge for the Mercury, who were swept by the Aces in last season’s WNBA Finals. This was the Mercury’s largest margin of victory since defeating Indiana 95-60 on Aug. 7, and it’s the Aces’ worst defeat since a 111-58 loss to Minnesota on Aug. 3. Las Vegas then finished the regular season with 16 consecutive wins.

Phoenix opened the season 1-0; Las Vegas fell to 0-1.

Thomas, a forward, played 26 minutes and added six rebounds and nine assists. She shot 8 of 15 from the field and made 4 of 5 free throws. Her all-around performance — scoring, playmaking and relentless pressure on defense — set the tone for a Mercury team that never trailed.

Natasha Mack, a forward, recorded 10 points and 15 rebounds in 25 minutes, grabbing seven offensive boards and adding one assist and one block. DeWanna Bonner, a forward, contributed 13 points, seven rebounds, two assists and two blocks in 22 minutes. Kiana Williams, a guard from San Antonio, Texas, came off the bench for 11 points on 4-of-10 shooting, including 3 of 8 from three-point range, in 21 minutes.

For the Aces, center A’ja Wilson scored 19 points on 8-of-16 shooting with four rebounds, four assists and two blocks in 24 minutes. Forward NaLyssa Smith from Converse, Texas, added 11 points and six rebounds. Guard Jackie Young had 12 points, six rebounds and three assists but shot just 5 of 14 from the floor. Guard Chennedy Carter from Fort Worth, Texas, scored 10 points and had two rebounds and two assists.

Phoenix shot 38 of 77 from the floor, 11 of 24 from three-point range and 12 of 15 from the free throw line. Las Vegas shot 29 of 71 overall, 4 of 19 from deep and 4 of 8 at the stripe. The Mercury outrebounded the Aces 40-36, forced 17 turnovers while committing only seven, and recorded 11 steals to Las Vegas’ five.

The most important part of the game came in the second quarter, when Phoenix turned a six-point lead into a 20-point halftime advantage. Leading 27-21 after one quarter, the Mercury opened the second period with a 12-2 run. Jovana Nogic converted a three-point play, Natasha Mack scored inside, and Alyssa Thomas and DeWanna Bonner added baskets. The Aces managed only 14 points in the quarter while Phoenix poured in 29. Las Vegas surrendered 10 offensive rebounds in the first half, and the Mercury capitalized with 14 second-chance points. By halftime, Phoenix led 56-35.

The Mercury’s defense smothered the Aces in the third quarter, holding them to 10 points while scoring 27. Phoenix built the lead to 83-45 entering the fourth. Las Vegas never got closer than 31 points the rest of the way. The 33-point victory was the largest margin of defeat for the defending champions since that 53-point loss to Minnesota nearly three years ago.

Key plays defined the decisive second quarter. With 7:24 left, Nogic hit a 26-foot three-pointer off a Thomas assist to push the lead to 15. Less than a minute later, Thomas stole a pass from Jackie Young and fed Bonner for a fast-break layup. After a timeout, Wilson answered with a turnaround jumper, but Thomas answered with a layup, and Bonner buried a 25-foot three-pointer to make it 48-31. The Mercury closed the half on a 12-4 spree, capped by Nogic’s 25-foot three with 30 seconds left.

Phoenix’s offensive rating of 117.7 points per 100 possessions dwarfed Las Vegas’ 76.9. The Mercury assisted on 11 of their 38 field goals, turned the ball over just seven times, and committed only 10 fouls. Las Vegas had five assists and 17 turnovers, a ratio that spelled doom against a focused Mercury defense.

Thomas was the top star for Phoenix. Her 20 points came on efficient shooting, and her nine assists orchestrated an offense that moved the ball crisply. She also grabbed six rebounds and collected two steals, repeatedly picking off Aces passes and igniting transition opportunities. Mack’s 15 rebounds — seven on the offensive glass — gave Phoenix extra possessions and wore down Las Vegas interior defenders. Bonner’s 13 points included two three-pointers, and her two blocks helped hold the Aces to 39 percent shooting overall.

The Aces struggled to find rhythm. Wilson was the only Las Vegas starter to score in double figures; Young shot 5 of 14, and the rest of the starting lineup combined for 18 points on 7-of-22 shooting. The Las Vegas bench outscored its Phoenix counterpart, but the damage was done early.

The attendance was 16,511 at Mortgage Matchup Center in Phoenix, Arizona, though the Mercury were designated the visiting team. The game marked an emphatic opening statement for Phoenix, which avenged last year’s Finals sweep in dominant fashion. The Mercury next face the Golden State Valkyries on Sunday, while the Aces travel to Los Angeles to meet the Sparks on the same day.

Interstat’s ELO system had projected Las Vegas with a 79.60 percent probability to win. Las Vegas had been installed as a pregame favorite with a spread of -7. The total score of 99 went over the over/under line of 165.5.