An entirely forgettable first half saw very few chances at both ends as the rain lashed down on South London. Slick passing was impossible in midfield with the ball spending the majority of the time up in the air.
Grabben lashed a teasing volley across goal that Karl Broadhurst did well to clear in front of the advancing Marc Laird 12 minutes in. The hosts kept the ball well and looked in control, but failed to carve the resolute Bulls defence open.
Neil Harris twisted and turned himself into space down the Lions left before chipping to the back post only for Tresor Kandol to nod tamely wide.
The feisty and forgettable encounter was sparked into life with midfielders from both sides seeing red shortly after half-time.
Nadjim Abdou was the first to see red for a reckless two-footed challenge on winger Clint Easton just three minutes after the interval.
Nick Chadwick controversially followed shortly after having been handed two harsh yellow cards seven minutes apart, the first for kicking the ball away and the second for a strong challenge that floored both Dave Martin and frontman Kandol.
Andy Frampton almost grabbed a winner on 85 minutes as he watched his diving header whistle inches over the bar from Grabban's teasing cross.
The young winger grabbed his goal 60 seconds later having powered home the rebound from his own low effort that gave keeper Darren Randolph with no chance.