Eddie Nketiah struck late to hand Arsenal a 2-1 victory against Bundesliga champions Bayern Munich in their International Champions Cup opener in Los Angeles.
Bayern looked to be on course for a draw in LA after Robert Lewandowski's 71st-minute strike cancelled out Louis Poznanski's own goal (49).
But Unai Emery's side snatched victory as substitute Nketiah netted in the 88th minute to hand Arsenal their second win of pre-season following their 3-0 win against Colorado Rapids on Tuesday.
How Arsenal stunned Bayern
Bayern created the first real chance of the game at Dignity Health Sports Park as David Alaba's cross picked out Thomas Muller, but the German forward was denied at close range by a superb stop from Bernd Leno.
Arsenal team news
Starting XI: Leno, Maitland-Niles, Mustafi, Sokratis, Monral, Xhaka, Willock, Mkhitaryan, Ozilm Aubameyang, Lacazette.
Subs used: Martinez, Kolasinac, Nelson, Burton, Chambers, Saka, John-Jules, Nkeitah.
Niko Kovac's side then needed Manuel Neuer to keep the scores level as Pierre-Emerick Aubameyang sprung forward to set up Mesut Ozil, and the former Germany international saw his effort parried away by Neuer.
The Gunners took the lead minutes into the second-half when Poznanski, who had only just come on, diverted Aubameyang's cross into his own net.
Bayern were almost back on level terms just minutes later. Former Arsenal man Serge Gnabry raced through on goal before a brilliant hand from Emiliano Martinez, who replaced Leno at half-time, stopped him from levelling the scores.
The equaliser did eventually come and Gnabry was involved once again as his cross found the head of Robert Lewandowksi, who made no mistake.
With the game appeared to be heading for a draw Arsenal struck late on when Tyreece John-Jules exchanged passes with Calum Chambers before picking out Nketiah, who snatched a dramatic late winner.
What we learned?
Sky Sports' Oliver Yew: Pre-season can often be misleading with teams experimenting ahead of the new season, but did Emery give us glimpse into his plans for the new season with Arsenal's 2-1 win over Bayern Munich?
Reports have suggested Granit Xhaka is the leading candidate to replace Laurent Koscielny as Arsenal captain after the Frenchman refused to go on the club's pre-season tour of America and he was given an early chance to impress in the role, playing the full 90 minutes with the armband.
Another player given the chance to impress was Joe Willock and he made the most of it.
Starting alongside Xhaka in midfield, the 19-year-old produced an eye-catching display against the German champions. He was assured on the ball and wasn't afraid of the physical battle which will have impressed Emery.
Arsenal have an exciting crop of youngsters coming through the ranks and they are getting their chance to shine on this pre-season tour.
Willock, Nketiah and Reiss Nelson are some of the more well-known names but Bukayo Saka, James Olayinka, Tyreece John-Jules and Robbie Burton have all played a part against Colorado Rapids and Bayern Munich.
Emery has praised the impact of new assistant coach Freddie Ljungberg as Arsenal give youth chance in America.
"[It's been] very positive," Emery said after Arsenal's win over Bayern. "We worked last year with Steve Bould, Freddie with the U23s. We changed because for them it was a good option.
"With Freddie we are working. Above all he's helping us with the young players because he knows better than us every young player.
"For example, Robbie [Burton]. I didn't know Robbie. Freddie said to me he's a good player with the capacity to play as a six or eight. Really, he helped us."
Emery: Young players will get chances
Arsenal head coach Emery was pleased with the performances of his young players against Bayern Munich and insists they will continue to get chances to impress in pre-season, starting on Saturday against Fiorentina.
"We have the responsibility with the young players to give them chances," the Spaniard said.
"We want to use different young players to help. Some players will be with us in pre-season, some players will be with us in the season.
"Each minute they show their performance against big players. For example, the one-to-one [Eddie] Nketiah against [Niklas] Sule showed how he can respond.
"Today was very positive."
When asked if he will rely more on the young players, he added: "It depends on their performance. Against Colorado Rapids a lot of young players played. We need them for the moment but also in the future.
Our responsibility in this club for the history, present and future is to give young players chance. If they deserve minutes they'll get minutes. I'm very happy with them and their work.
"We are going to play against Fiorentina on Saturday and will use young players. It's another chance for them to show us how they can respond."
July 20: Fiorentina - Bank of America Stadium, Charlotte
July 24: Real Madrid - FedEx Field, Washington DC
July 24: Barnet - The Hive
July 28: Lyon (Emirates Cup)
July 31: Angers - Stade Raymond Copa
August 4: Barcelona (Joan Gamper Trophy) - Nou Camp