They surpassed the previous record of 263-5, set by Royal Challengers Bangalore in 2013
Chasing 276, the visitors were bundled out for 155 within 33 overs in Multan as Nawaz excelled with his spin bowling and finished with career-best ODI figures of 4-19. Mohammad Wasim also chipped in, taking 3-34 on his comeback.
Earlier, Pakistan captain Babar Azam (77) and opener Imam-ul-Haq (72) formed a formidable partnership of 120 for the second wicket to hand the hosts a par score after they opted to bat.
Pakistan, who won the opening match by five wickets, will look to complete a clean sweep of the series when the third ODI takes place on Sunday.
They have now won 10 consecutive ODI series against the West Indies.