Hafeez struck a majestic 140 not out off 136 balls in the third one-day international on Sunday as the hosts raced to 5-326 off their 50 overs - the highest day-night total in Sharjah – and then took 2-35 to help bowl Sri Lanka out for 213.
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The 33-year-old was ably supported with the bat by opener Ahmed Shehzad (81) and captain Misbah-ul-Haq (40) as Pakistan scored at 6.52 runs per over.
A quickfire 23 off 12 deliveries from Umar Akmal gave Pakistan a late spurt of runs, with only Thisara Perera (2-58) causing problems with the ball on a tough day for the tourists.
Sri Lanka's run chase began badly with the dismissal of Kusal Perera and Dimuth Karunaratne in the fourth over at the hands of Umar Gul (3-19), as Pakistan produced some fine limited-overs bowling.
Tillakaratne Dilshan (59) and Dinesh Chandimal (36) tried to get Sri Lanka back on track as they put on 59 for the fourth wicket, but they both fell within six overs of each other.
Junaid Khan (2-40) and Gul both did damage at the top of the order, while Shahid Afridi (1-31) removed dangerman Dilshan as he squeezed a delivery under the 37-year-old's bat.
Sri Lanka's collapse then began as they lost five wickets for 81 runs.
Saeed Ajmal (2-37) got himself in on the act with two late dismissals to take his tally for the year to 103 wickets and set a new record for the most in a year by a Pakistani – beating Saqlain Mushtaq's 1997 haul.
Visiting captain Angelo Mathews (44) valiantly tried to keep his side in contention, but he was Ajmal's second victim and Sri Lanka's defeat was confirmed when Gul removed Lasith Malinga's middle stump the defeat was confirmed.