It was the second-highest opening partnership in ODI history, falling two runs short of Sri Lanka's 286 in 2006.
Warner hit 179 off 128 balls while Head made 128 off 137 balls.
Both batsmen hit their best ODI scores as Australia closed on 369-7. Babar Azam scored 100 in Pakistan's 312-9.
However, the tourists were never really in the hunt for victory on Australia Day as wickets fell at regular intervals - Mitchell Starc taking 4-42.
Victory completed a 4-1 series win for Steve Smith's Australia side, who will now fly to Auckland to face New Zealand in a three-match ODI series.
"We've played some pretty good cricket over the last couple of games," reflected Smith. "Davey Warner has been absolutely outstanding, and I thought Travis Head played very well to get his first ODI hundred."
Australia's David Warner and Travis Head put on 284 for the first wicket to lay the foundations for a 57-run victory over Pakistan in the fifth one-day international in Adelaide.