Royals took just three minutes to go behind to a James McClean opener before Steve Fletcher's smart finish doubled Sunderland's lead in Tuesday night's rearranged match.
The visitors did put up a fight in the second period but Stephane Sessegnon struck a third in injury time to earn Martin O'Neill's side their first home Premier League win of the season which lifted them out of the drop zone.
Reading, meanwhile, are left with a mountain to climb with Brian McDermott's men entrenched in the bottom three and six points from safety entering the festive period.
However, it doesn't get any easier for the Royals who entertain Arsenal next Monday then go to champions Manchester City the following weekend.
Meanwhile, pressure is mounting on McDermott to turn the team's fortunes around, though the manager this week received the full backing of Reading chairman Sir John Madejski.
However, unconfirmed reports were circulating after the game linking Royals with former assistant manager Wally Downes.
Downes, 51, left his post as Sam Allardyce's first-team coach at West Ham by mutual consent on Tuesday night.
The former Crazy Gang member was Steve Coppell's assistant when Reading were last in the Premier League and left the Madejski Stadium along with Coppell in 2009.
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