After 14 years at Lyon, Lacazette decided it was time to move on and was reported to have agreed to join up with his France team-mate Antoine Griezmann at Atletico Madrid.
However, Atletico then had a transfer ban upheld over the signing of foreign minors and with the Madrid club barred from registering new players until January 2018, Arsenal stepped in.
A dead-eyed finisher, the 26-year-old was the top-scoring Frenchman in each of the last three Ligue 1 seasons and left Lyon having scored 113 goals in his last four campaigns.
He cost Arsenal an initial fee of £46.5 million ($60.6 million, 51.6 million euros), making him both Arsenal's biggest ever signing and Lyon's biggest ever sale.
Morata has scored in a Champions League final, netting for Juventus in their 2015 loss to Barcelona, but arrives after a frustrating season as a back-up player at Real Madrid.
Tottenham Hotspur manager Mauricio Pochettino has claimed Morata was deterred from joining Spurs two years ago due to his fears about the competition he would face from Harry Kane.
But despite the striker's inability to dislodge Karim Benzema from the Madrid starting XI, Chelsea manager Antonio Conte believes he can reach the very top.
Arsenal blew Chelsea away with a sensational display, Aaron Ramsey's 79th-minute winner securing a 2-1 win that brought the beleaguered Wenger a record seventh success in the competition.
Will we see a repeat of that performance or will Conte and his men come back to take revenge?
Full time, it's finished here 1-1. We will now go to penalties. Both the goals coming in the second half, Moses had given the lead to the blues before Pedro received his marching orders. Kolasinac equalised from the resulting free kick. Arsenal were slightly the better team over 90 minutes, but Chelsea did have a strong second half.
We ahve reached half-time here, and it's 0-0 here. Lacazette coming closest with his shot hitting the post. Arsenal have been the livelier of the two teams so far, Chelsea not closing down quickly enough in key areas. Both teams will be hoping for a better performance in the final third. Do join us for the second half!
18 Oct, 2017 | Pakistan and Sri Lanka in UAE SL vs PAK 208/1048.2 overs 209/342.3 oversPakistan beat Sri Lanka by 7 wickets
18 Oct, 2017 | Bangladesh in South Africa SA vs BAN 353/650.0 overs 249/1047.5 oversSouth Africa beat Bangladesh by 104 runs
16 Oct, 2017 | Pakistan and Sri Lanka in UAE PAK vs SL 219/950.0 overs 187/1048.0 oversPakistan beat Sri Lanka by 32 runs
15 Oct, 2017 | Bangladesh in South Africa BAN vs SA 278/750.0 overs 282/042.5 oversSouth Africa beat Bangladesh by 10 wickets
13 Oct, 2017 | Pakistan and Sri Lanka in UAE PAK vs SL 292/650.0 overs 209/850.0 oversPakistan beat Sri Lanka by 83 runs