The Sky Blues drew 1-1 with Group H leaders Kashima Antlers in Japan on Tuesday night, falling behind to another set piece before an improved second-half display paved the way for Simon's 70th-minute equaliser.
It was the pugnacious striker's first ACL goal in nine years and one that could yet help the reigning A-League champions return from the brink.
That will depend how second-placed Suwon Bluewings fare against third-placed Shanghai Shenhua later in matchday four.
With two home defeats, two away draws and an unenviable goal difference, Sydney's chances of progressing from dead last remain slim, and Alex Brosque will rue skewing a shot agonisingly wide with 15 minutes remaining.
Arnold wasn't lying when he said he'd play some youngsters in the absence of regular stars Milos Ninkovic, Bobo, Michael Zullo and Brandon O'Neill, handing Chris Zuvela his competitive debut and Anthony Kalik his first start.
Judging by the sheer youth of Sydney's bench - all but Charles Lokolingoy had not played a single A-League minute this season - Arnold was prepared to sacrifice what sliver of continental hope remained in favour of seeing out his side's domestic domination before departing to coach the Socceroos.
For all that, it was two senior players at fault for Kashima's opener off a corner just before the half-hour mark.
A defensive mix-up between Brosque and Josh Brillante saw the latter head straight to Mu Kanazaki, who met the ball flush with his own head and didn't miss at the far post.
Apart from that blunder Sydney were not uncomfortable but, though they pushed and probed, were mostly pedestrian in attack.
Adrian Mierzejewski carved a rare opening just before halftime, flooding forward and playing in Kalik, but the 20-year-old's finish let him down.
With an hour gone and everything to do, Arnold introduced Lokolingoy and Sydney sparked.
It pre-empted Mierzejewski's next foray and the Polish winger, overlooked on Tuesday for an international recall, passed to Luke Wilkshire.
The fullback's cross was spot on and Simon headed home, just in time to earn his second yellow card of the tournament and a suspension for matchday five.
It may not have ended there, and Brosque's tight-angled finished practically brushed the outside of the far post before Simon came close and Leo Silva missed a late shot for the hosts.