The men's team boss Postecoglou, watching alongside club chairman Daniel Levy at the Tottenham Hotspur Stadium, must have feared the worst as he watched his fellow Australian Caitlin Foord hit the post with a fine run and shot in the 17th minute as Arsenal looked rampant.
But ultimately, despite having 31 attempts on goal to the home side's eight, unfancied Spurs battled hard to eke out a 1-0 win on Saturday (Sunday AEDT) thanks to a fine team move finished by Martha Thomas just before the hour mark.
It meant deep frustration for Arsenal, with their three Matildas - Foord, Steph Catley and Kyra Cooney-Cross - all having hoped they might be celebrate going into Christmas with their side on top of the WSL.
Instead, after their brilliant 4-1 win over Chelsea the previous week, Arsenal, who remain on 22 points after 10 games, blew it to offer Sam Kerr's champions, also on 22 after nine, the chance to take control again when they visit Bristol City on Sunday (Monday AEDT).
It left Catley hugely disappointed. "Its extremely frustrating, it's a tough league and you can't afford to drop too many points," she told Sky Sports.
"We created big, big chances - and a lot of them too - and on another day, a lot of them, or just one, might have gone in.
"They had one chance and it went in. Football can be cruel sometimes.
"Today just wasn't our day, we'll have to regroup and come back stronger. It's a long season and we'll keep on fighting.
"We have to keep focusing on the next results and make sure we get points in every single game from here on."
It was an extraordinary result, considering how Arsenal had approached the game off the back of seven straight league wins and mid-table Spurs, who had shipped 11 goals in their last two league games, had never beaten their north London foes in seven previous WSL meetings.
Foord was at the heart of Arsenal's first-half domination but, despite her one brilliant moment when her cut-in and driving shot rattled the woodwork, she was guilty of some wasteful moments as she foraged down the left flank.
After Thomas had got on the end of a well-worked move that began deep in Spurs' own half in the 58th minute, Arsenal couldn't break down the home side, marshalled well by league debutant keeper Barbora Votikova.
Cooney-Cross had a late, goal-bound volley headed away close to her own line by Angharad James and moments later, Catley claimed to have been brought down by the same defender in the box, prompting boos from the Spurs faitfhul.
The game was paused late on for a medical emergency in the crowd but when supersub Vivianne Miedema hooked over in the first minute of 11 added on, all was lost for Arsenal.
