Sydney FC dug deep to grab a point in front of nearly 20,000 at Parramatta Stadium - and was on course for a second derby win over WSW this season before former Sky Blue Shannon Cole curled home a 70th minute equaliser.
Talisman Alessandro Del Piero gave Sydney a 36th minute lead but the visitor was shaken up by the 56th minute red card shown to skipper Brett Emerton as it denied WSW an eleventh straight A-League win.
And it finally caved in when Cole punished by foul by Adam Griffiths on Dino Kresinger with a curling dead ball which flew in past keeper Ivan Necevski diving to his right.
The point leaves WSW six clear of second-placed Central Coast, which still has two games remaining, and on the cusp of the crown.
It was also vital for Sydney FC, which moved into fifth spot and looks set for the play-offs going into its final regular season game against Brisbane at Suncorp Stadium next weekend.
Sydney led thanks to a gaffe from Nikolai Topor-Stanley, who has been imperious for the Wanderers at the back this season.
But he dallied on the ball before delivering a suicide pass to the feet of Del Piero, who gleefully accepted, surging into the penalty area to fire past keeper Ante Covic with his left foot.
In a match of few chances - and high tension - former Sky Blues striker Mark Bridge could have bagged an equaliser just 60 seconds later but his shot was tipped-away by keeper Ivan Necevski after Shinji Ono had crafted the opening.
The Sky Blues - hit by a spate of send-offs this season - found themselves up against it again when skipper Emerton was handed a straight red card by referee Kris Griffiths-Jones in the 56th minute after a reckless, studs high, lunge on Cole.
Cole saved WSW late on by denying substitute Yairo Yau a winner with a crucial interception.
There was late drama when makeshift defender Iacopo La Rocca was shown a straight red for a swinging elbow to the face of Terry Antonis to take the tally to nine yellows and two red cards on the night.
"I thought we were in control right up until the red card (to Emerton)," said Sydney coach Frank Farina.
"We were looking comfortable and not really in any danger. That changed it for us.
"We've shown we finish games strongly, even with 10 men."
"Some of the yellow cards for both teams tonight were soft. In a spectacle like this, in a big game like this, I thought it was an under-par performance.
"People want to see an even contest. For 30 minutes at the end it wasn't an even contest, but at least we managed to get a draw, so I'm happy with that."
Wanderers coach Tony Popovic said of the outcome: "The message we've given the players is that we've gone a step closer. We're six clear now and continuing our unbeaten run to 11 games and we move on to next week.
"I think derbies are difficult, regardless of who is playing, but the players that came in (following a spate pf injuries) were fantastic."