Smith and Leishman carded a final round 70 in the alternate-shot format on Sunday to finish at 20-under 268, along with third-round leaders Louis Oosthuizen and Charl Schwartzel (71).

Oosthuizen's tee shot found the water on the par-5 18th on the first extra hole with Smith sinking the winning putt to secure his second title at the event in four years – having won his maiden PGA Tour title in 2017 playing with Swede Jonas Blixt.

Smith's third career win on the lucrative US Tour and Leishman's sixth netted them US$1.069 million (AU$1.35m) each in prize money.

With Adam Scott electing to skip the Tokyo Olympics this year to spend time with his family, it appears most likely that Smith and Leishman will team up again to represent Australia when at the rescheduled Games.

The climactic finish at TPC Louisiana in New Orleans rounded off a compelling duel between two teams that teed off together in the final grouping and took turns holding leads that never grew to more than two strokes.

Leishman and Smith were full of laughs this week at TPC Louisiana. PHOTO: Mike Ehrmann/Getty Images.

Starting the day a shot behind major champions Oosthuizen and Schwartzel, Smith and Leishman drew level with their third birdie on the front nine before they took a two-shot advantage when they birdied the par-5 11th.

However, bogeys on 13 and 15 resulted in them trailing by one shot.

A key moment arrived on the short par-4 16th, with Leishman chipping in for birdie after Smith's drive dribbled into the water short of the green.

Both pairs made bogey on the par-3 17th and pars on the closing hole to force the playoff.

Smith is now 3-0 in playoffs on the PGA Tour, having won the 2020 Sony Open on the first extra hole.

Peter Uihlein and Richy Werenski shot a 67 to shoot up the leaderboard from 18th to third at 19 under.

Billy Horschel and Sam Burns (69) tied for fourth with Brandt Snedeker-Keith Mitchell (69) and Brendan Steele-Keegan Bradley (70) and shot further back.

Ryan Palmer and Jon Rahm, the defending champions from 2019, closed with a 70 to finish seventh at 17 under.