FC Porto extended their unbeaten run to 50 matches on Friday evening.The Portuguese table-toppers battled back from 2-0 down against title rivals Sporting Lisbon to earn a priceless 2-2 draw at the Estadio do Dragao.Sporting raced into a 2-0 lead in the first half thanks to goals from Paulinho and Nuno Santos.Porto halved the deficit just before the half-time interval courtesy of Fabio Vieira's strike and they finally found an equaliser in the 78th-minute of play.Mehdi Taremi was the man who delivered it, the home side taking advantage of the fact that Sporting were down to 10-men because former Liverpool defender Sebastian Coates picked up a second booking four minutes after the break.It was a thrilling match all in all, but things descended into chaos at full-time.Ex-Real Madrid defender Pepe was, of course, at the heart of it.In the ninth and final minute of stoppage-time, the seemingly ageless centre-back appeared to take a blow to the head inside the penalty area from Joao Palhinha's acrobatic clearance.Pepe writhed around in agony for close to a minute while being ignored by the referee and watching play continue.The full-time whistle then kickstarted the chaos, with players and staff all heading towards the goalmouth where Pepe was.And for a good five minutes inside the Dragao, it was absolute mayhem. Four players (Pepe, Palhinha, Tabata and Agustín Marchesín) were shown red cards by the referee for their part in a 40-man brawl that even involved the ball boys.Check out footage of the wild scenes on the pitch at full-time here...

Video: The chaos after Porto 2-2 Sporting

Pepe escaped a red card for his part in the initial brawl, but was eventually given his marching orders for getting involved in another spat when things appeared to be cooling down.

The Porto ball boys certainly didn't help matters either, one of them inexplicably shoving Sporting's Matheus Reis. He was eventually dealt with by the stewards.

You get the feeling retrospective action will follow once the Portuguese footballing authorities have analysed the melee in full and found those who escaped punishment at the time.

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Porto will still be happy with the draw, though, a result that keeps them six points ahead of Sporting at the top of the table.