Sporting were seconds away from holding on to victory in their Europa League Group G clash against Genk, despite playing for half an hour with 10 men in Lisbon.
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The hosts had Stijn Schaars sent off for a second yellow card just before the hour mark but rallied to take the lead through Ricky van Wolfswinkel just six minutes later.
They held on their advantage until the first minute of injury-time when Glynor Plet headed the Belgian side level.
A share of the spoils is of little use to Sporting, who sit bottom on group on two points, but Genk saw their hopes of topping the table boosted as they moved two clear with eight points from four games.
The visitors began well, Thomas Buffel looking for his range with a curling effort from outside the area and Jelle Vossen sending a bullet header wide, much to Rui Patricio's relief.
Neither side managed to end the stalemate before half-time, though, with Valentin Viola's high attempt the last before the break.
Sporting came out strongly, Emiliano Insua narrowly missing with a fine effort then heading wide from a 55th-minute corner.
Soon after, Schaars fouled Buffel and received his marching orders.
But instead of handicapping the hosts, they responded with the opener. Van Wolfswinkel met Diego Capel's cross with a strong downward header and the 10 men took the lead.
Genk were determined to find an equaliser, Anele Ngcongca twice working Patricio in the space of four minutes and Vossen again off target from 25 yards.
Zakaria Labyad almost extended Sporting's lead with a superb long-range volley that was well saved by Kristof van Hout before Patricio produced a fine stop of his own to deny Ayub Masika.
That looked to be enough until the 91st minute when Buffel's run and cross found Plet at the far post and Genk snatched a late draw.