Arsenal missed out on the chance to hoist themselves into third place in the Premier League table alongside defending champions Manchester City.
The Gunners eased into a 2-0 lead thanks to Pierre-Emerick Aubameyang’s two first-half goals at Vicarage Road.
However, Arsenal produce a woeful second-half performance as Tom Cleverley and Roberto Pereyra levelled the Premier league clash.
Watford were unfortunate not to secure three points given the north London side’s abject display after the break.
Arsenal struggled to find their passing rhythm in the second half as Watford registered over 20 shots on Bernd Leno’s goal.
Former Liverpool FC captain Souness was left staggered by Arsenal’s collapse in the second 45 minutes.
“Their manager after that game will be thinking that he has two different teams,” Souness said on Sky Sports. “They capitulated in the second half, Arsenal, they didn’t win a challenge.
“If you’re an Arsenal supporter watching that you must be scratching your head, it was two different teams.
“Proper teams don’t play like that, proper teams don’t have a half like the first half and then play like that in the second half, proper teams just don’t do that.
“They were bringing on kids, that was a game where at 2-1 it was time to dig in and regroup and make sure they’re not going to lose the game.
“When the kids came on they were all over the place, it was like a game of basketball. If you’re an Arsenal supporter that would deeply worry you, they were so bad in the second half.”
Arsenal signed Chelsea FC defender David Luiz in the summer to bolster their back four.
However, the Gunners have already conceded eight times in five games in the Premier League this season.
Unai Emery’s men will take on promoted side Aston Villa at The Emirates in their next Premier League fixture on Sunday afternoon.
Arsenal have failed to finish in the top four in the last three Premier League seasons.
The Gunners will make the trip to Eintracht Frankfurt in their first Europa League game on Thursday night.
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