Bukayo Saka eventually scores the rebound, giving Arsenal a commanding 3-0 lead over Chelsea, after a string of saves from Mendy.
Gabriel Jesus continued his hot scoring streak as Arsenal humiliated a poor Chelsea team in Orlando.
The Gunners’ Brazilian striker scored his fourth goal in four pre-season games with a delightful 15th minute opener.
Skipper Martin Odegaard added a second in the 36th minute before Bukayo Saka and Sambi Lokonga also scored after the break in a promising performance by Mikel Arteta’s side.
Thomas Tuchel’s Blues meanwhile were woeful, and look a team lacking confidence and rhythm in a worrying result.
This drubbing comes just days after they lost to MLS newbies Charlotte FC on penalties, while they scraped past Club America in Las Vegas.
German coach Tuchel will now be hoping for several new faces before the start of the new campaign to lift the mood at the club.
Both teams flew back to the UK after the full-time whistle with Arsenal the ones looking ready to hit the ground running this season.
Oleksandr Zinchenko got his appearance start in an Arsenal shirt at left wing-back despite only joining up with the squad in Orlando on Friday having completed his Manchester City move.
Much has been made about how Mikel Arteta will use Ben White, William Saliba and Gabriel Magalhaes this season, but on this occasion he started the trio in a back three.
For Chelsea, Raheem Sterling was handed his maiden start while fellow new-boy Kalidou Koulibaly sat on the bench.
For the first time in pre-season, Tuchel played practically his strongest line-up available but was left incredibly frustrated as they were given the run-around by an efficient Arsenal.
From a Chelsea corner, Gabriel Martinelli intercepted and broke from his own box before playing in Bukayo Saka whose shot was fired straight at Mendy.
In an attempt to disrupt Arsenal’s flow, Chelsea began landing some heavy tackles to the disdain of Arteta, in particular after Conor Gallagher’s swipe at Saka.
But Tuchel’s men were causing their own problems thanks mostly to Mendy’s poor distribution and a back four that were struggling to pick out a pass.
The two issues combined in the 15th minute as Trevoh Chalobah’s wayward pass was snapped up by Granit Xhaka and his first-time ball put through Jesus.
One touch is all the Brazilian needed before chipping over an on-rushing Mendy.
Tuchel was angry and animated with his players during a brief water break.
Yet Arsenal continued to build momentum as Odegaard’s whipped free-kick nearly caught out Mendy, but the Senegalese keeper was at fault for the north London club’s second.
With nine minutes remaining in the half, Mendy’s chipped punt found a player in red as Martinelli swivelled before poking Odegaard in behind to calmly slot home.
Chalobah was out of position once more, and hobbled off just before the break for Malang Sarr, despite Koulibaly’s presence on the bench.
The Blues ended the half brightly with Mason Mount smacking Aaron Ramsdale’s post, but that was all the England international had to worry about.
Arsenal made just the one change at the break, Zinchenko being replaced by Nuno Tavares at left-back, while Tuchel made sweeping alterations to his team.
Switching to a three at the back, Cesar Azpilicueta came on alongside Marcos Alonso, Mateo Kovacic and Christian Pulisic for Sterling, Emerson, Conor Gallagher and Timo Werner.
Throughout the half, both sides broke up the game with further changes, most notably Koulibaly’s arrival for his first minutes in a Chelsea shirt as he showed glimpses of his quality.
While Chelsea improved with the switch of formation, Arsenal continued to look dangerous on the break and grabbed a deserved third through Saka in the 66th minute.
Mendy was forced into two saves to deny Martinelli and Xhaka before Saka fired the rebound into the roof of the net at the third attempt.
In injury time, a superb cross by Cedric Soares found Lokonga at the far post to head back across Mendy.
ARSENAL: (4-2-3-1) Ramsdale; White, Saliba, Gabriel, Zinchenko; Partey, Xhaka; Saka, Odegaard, Martinelli; Jesus
CHELSEA (4-3-3) Mendy; James, Chalobah, Silva, Emerson; Mount, Gallagher, Jorginho; Sterling, Havertz, Werner
Watch Bukayo Saka 3rd Goal for Arsenal vs Chelsea below;
