Club-record signing Lacazette netted a goal in either half - including one from the penalty spot - as the Gunners moved into seventh position in the Premier League table.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
ARSENAL: Cech; Mustafi, Koscielny, Monreal; Bellerin, Elneny, Xhaka, Kolasinac; Ramsey, Sanchez; Lacazette
WEST BROM: Foster; Nyom, Evans, Hegazi, Dawson, Gibbs; Livermore, Barry, Krychowiak; Robson-Kanu, Rodriguez
6 - Arsenal have won each of their last six Premier League games at the Emirates Stadium vs West Brom, conceding just one goal. Routine. pic.twitter.com/jeyF8u5DSf— OptaJoe (@OptaJoe) September 25, 2017