Spoiling the occasion of Gareth Barry’s record 633rd Premier League appearance, his two goals also ensured a continuation of Arsenal’s 100 percent record at the Emirates so far this season and wider run of eight consecutive home league wins.
In only the fifth minute, having been brought down by Craig Dawson on the edge of the area, Sanchez bent a free kick just wide of the right post.
The visitors swiftly responded when a classy through-ball from Barry sent Jay Rodriguez into space on the left. The forward was unfortunate not to be awarded a penalty when brought down by Shkodran Mustafi’s cumbersome challenge, but after returning to his feet he forced Petr Cech into a fine save when the goalkeeper tipped his low shot onto the post.
Mohamed Elneny, starting his first Premier League fixture since the season’s opening day in perhaps a demonstration of Arsene Wenger’s wariness of West Brom’s physical threat, then briefly took responsibility for Arsenal’s creativity. His ball wide was volleyed by Hector Bellerin towards Aaron Ramsey, who despite space at the near post could only head high and wide.
The midfielder was then brought down by Jonny Evans, among Wenger’s summer transfer targets, also on the edge of the area, to win the 20th-minute free-kick that produced their opening goal. On this occasion Ben Foster tipped Sanchez’s curling effort away, but with the goalkeeper on the floor, Lacazette was the quickest to respond and instinctively headed low into the near open goal.
West Brom, largely outclassed by their composed hosts, were unfortunate not to level in the 38th minute, again through Rodriguez. After Grzegorz Krychowiak broke down the left and hooked a cross towards the forward, Rodriguez succeeded in heading past Cech but could only watch as the recovering Nacho Monreal cleared off the goal-line and out for a corner.
The £52million Lacazette had had another dangerous, goal-bound shot blocked early in the second half before, in the 67th minute, the opportunity presented itself to him to seal all three points.
Allan Nyom clumsily brought down Ramsey inside the area and, with Sanchez still on the pitch, Lacazette stepped up to finish into the bottom-right corner beyond the diving Foster.
He was eventually replaced by Olivier Giroud in the 83rd minute, by which point victory appeared secure, but after Arsenal’s inconsistent start to the season the striker had taken his side up to seventh, with his fourth goal in five league starts.
Defeat also meant West Brom fell to 12th, but if Tony Pulis felt frustrated, Wenger had been rewarded by the 26-year-old Lacazette vindicating the hosts’ long-term pursuit
