Updated Sep 18, 2015 at 2:07a ET
PHOENIX — Brittney Griner raised the WNBA Defensive Player of the Year trophy just before tipoff and then showed why she received the honor.
Griner had 18 points and a WNBA playoff-record 11 blocks to lead the Phoenix Mercury to an 88-55 win over the Tulsa Shock on Thursday night in the opener of the Western Conference semifinals.
Griner, selected the league's top defender for the second straight year, also had eight rebounds.
"I try to go for that," Griner said of the defensive player award. "That's the one I try to get. I just want to show why I won it."
Griner, who led the league in blocks with 105 this season, broke her own single-game postseason record and shot 5 for 7 from the field and 8 for 9 on free throws.
DeWanna Bonner added 15 points for the defending champion Mercury.
Phoenix, the No. 2 seed in the West, hasn't lost a first-round playoff series since 2000 and is 10-1 all-time in a playoff series after winning the first game.
"We are hitting our peak at the right time and that's what you want going into the playoffs, feeling good about yourself," Mercury coach Sandy Brondello said. "It all starts with defense with me."
Phoenix took control of the game in the second quarter, turning a seven-point lead to a 30-point advantage at halftime. The Shock shot just 3 for 22 from the field while getting outscored 30-7 in the second quarter.
Odyssey Sims led Tulsa with 18 points and Jordan Hooper had 14 points and six rebounds. Plenette Pierson added 10 points and also had six boards.
Game 2 of the best-of-three series is Saturday in Tulsa.
"We just have to shoot the ball better," Tulsa coach Fred Williams said. "Brittney was just on rhythm. She's a hard guard for any team in this league and we know that. So we just have to continue to find ways to get her away from the rim."
Tulsa's Odyssey Sims (left) shoots over the Mercury's Brittney Griner during Thursday's opening game of a WNBA Western Conference semifinal series.
This is the Shock's first playoff appearance since moving to Oklahoma from Detroit before the 2010 season, and the team is relocating to the Dallas-Fort Worth area next season.
Griner, who was suspended for the season's first seven games, blocked three shots in the first quarter before leaving with two fouls. She converted a pair of three-point plays and led the Mercury on both ends of the floor with her offense and defense.
Phoenix led 22-15 at the end of the first quarter with Tulsa shooting 7 for 23.
The Mercury extended its lead to 13 points to open the second quarter after two 3s by Leilani Mitchell, who finished with 12 points and six assists. Mitchell then set up Mistie Bass for a layup in transition for a 30-17 lead.
"We just did a good job of making the extra pass," said Mitchell, who signed with Phoenix in the offseason. "That's one of the reasons that I'm here, is to knock down open 3s."
Tulsa went almost 4 1/2 minutes without a point in the quarter. Bonner hit a corner 3 and a reverse layup during that stretch as Phoenix went on an 11-0 run and led 52-22 at halftime.
The Shock pulled 56-38 on a 3 by Sims with 4:23 left in the third quarter. But Mitchell made a 3 as the shot clock expired with 1:19 left to put Phoenix up 65-40.
The Shock never got closer than 23 points the rest of the way.