The Milwaukee Bucks have squared up the NBA Finals at 2-2 after a thrilling 109-103 victory over the Phoenix Suns despite Devin Booker's 42-point haul on Wednesday.

The Suns led by six points at the final change but the Bucks, who trailed 2-0 in the series, stormed home led by Khris Middleton's 14 fourth-quarter points, finishing with 40 for the game.

Middleton starred with strong support from Giannis Antetokounmpo (26 points, 14 rebounds and eight assists) and Jrue Holiday (13 points, seven rebounds and seven assists).

After scores were level at half-time, Booker had piled on 18 points in the third quarter but Milwaukee made the key plays count in the final quarter.

Antetokounmpo made a crucial late block to deny Deandre Ayton from Booker's alley-oop lob, while Pat Connaughton came up with a key three-pointer.

Chris Paul had five turnovers for the game, including a late costly error which allowed Holiday to assist Middleton for two which put the Bucks four up with 27.2 seconds to play.

Phoenix shot better from the field, going at 51.3 per cent compared to Milwaukee's 40.2 per cent although they lost their radar late, but the Suns had 17-5 turnovers, with the Bucks scoring 24-5 points on turnover.

Middleton was a key influence for the Bucks, shooting 15 from 33 from the field along with three three-pointers, with six rebounds, four assists and two steals.

Middleton's 40-point haul was his postseason career high, while he outscored the Suns in the final two-minute stretch with 10-4 points.

Antetokounmpo put up 11 from 19 from the field at 57.9 per cent, while Brook Lopez chipped in a handy 14 points, although he and Holiday both missed all five of their three-point attempts.

Booker, who had his worst game of the playoffs in Game 3, responded with an excellent performance, shooting at 60.7 per cent from the field.

The young Suns guard almost fouled out late, with a non-call on a Holiday bucket with 3:30 to go but ultimately it would not be decisive.

Bucks at Suns

The NBA Finals series moves back to Arizona for Game 5 on Friday locked at 2-2.