Chelsea and Manchester United both won on Sunday to take the battle for the Premier League title to the final day of the season.
Gerrard was left with his head in his hands in the 33rd minute after his attempted backpass to Reina was seized upon by Didier Drogba, with the Ivory Coast international rounding goalkeeper Petr Cech before slotting home.
Chelsea doubled their advantage after the interval with Frank Lampard sliding the ball home from close range after Nicolas Anelka's low cross from the right.
It was Nani who settled United's nerves as he scored the only goal of the game just shy of the half hour mark.
Short passes on the edge of Sunderland's box between Ryan Giggs, Dimitar Berbatov, Wayne Rooney and Darren Fletcher and Nani angled a sumptuous low drive beyond Craig Gordon.
Chelsea host Wigan on the final day of the campaign next Sunday with a one-point advantage at the summit. United face Stoke at Old Trafford knowing only a win will put pressure on the Blues.