The Manchester City player displayed impressive agility and skill in both moves and passes, leading to an impressive 1-0 lead.
Arsenal manager Mikel Arteta expressed his satisfaction after thrashing West Brom 4-0 to complete three consecutive Premier League wins in eight days for the first time this season.
Before last weekend, the Gunners had gone eight league games without a win to find themselves languishing at the bottom of the points table.
“I’m so happy we were able to achieve the target that we had because the table looks completely different,” said Arteta, who had found his job under threat just four months on from winning the FA Cup.
“The energy we have around the place is much better and wins bring a lot of confidence. You can see that today in the way the team played.”
Arteta’s decision to finally put faith in his crop of talented youngsters has turned his side’s season around.
Sam Johnstone denied Hector Bellerin and Saka inside the first 10 minutes, but he was powerless to stop Tierney’s stunning opener on 23 minutes on Saturday.
Arsenal’s second was reminiscent of their flowing football at the height of the Arsene Wenger era as Saka fed Lacazette, whose brilliant pass played Smith Rowe in behind the West Brom defence and he squared for Saka to tap into an empty net.
The one way traffic continued after the break and some comical West Brom defending led to the third as Semi Ajayi smashed a dangerous cross off his own post and the ball broke to Lacazette to apply a simple finish.
Moments later another raid from Tierney down the left teed up Lacazette for another finish from point-blank range for his fourth goal in three games.
In another match of the day, Tottenham Hotspur beat Leeds United 3-0 as Son Heung-min scored his 100th goal for the Spurs.
The win propelled Jose Mourinho’s men back to the title challenge. They stand third with 29 points, four shy of joint table-toppers Arsenal and Manchester United.
With agency inputs