American Sebastian Korda returns the ball to France's Hugo Gaston during the ATP Next Gen tennis tournament in Milan, Italy on Nov 9, 2021. (ANTONIO CALANNI / AP)

American No 2 seed Sebastian Korda took advantage of the unique format of the Intesa Sanpaolo Next Gen ATP Finals, rallying from two sets down to defeat eighth-seeded Frenchman Hugo Gaston 3-4 (2), 3-4 (6), 4-0, 4-3 (3), 4-0 in the first day of group play Tuesday in Milan, Italy.

The ATP Finals employ a special first-to-four, best-of-five format, meaning four games win a set instead of the usual six.

Korda smashed 10 aces while saving nine of 10 break points. Gaston saved 13 of 18 break points.

Sebastian Korda is 1-0 in Group B along with No 6 seed Sebastian Baez of Argentina, who upset No 3 seed Lorenzo Musetti of Italy 4-1, 4-1, 3-4 (5), 4-3 (5)

In Group A, top seed Carlos Alcaraz of Spain swept Danish No 7 Holger Vitus Nodskov Rune 4-3 (6), 4-2, 4-0. No. 4 seed Brandon Nakashima of the US beat fifth-seeded Argentine Juan Manuel Cerundolo 4-1, 3-4 (3), 4-1, 4-0.

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Korda is 1-0 in Group B along with No 6 seed Sebastian Baez of Argentina, who upset No 3 seed Lorenzo Musetti of Italy 4-1, 4-1, 3-4 (5), 4-3 (5).

Stockholm Open

Entering the draw as a wild card, Andy Murray of Britain won his first-round match over Norwegian Viktor Durasovic 6-1, 7-6 (7) on Tuesday in Sweden.

Murray won 33 of his 39 first-service points. He led the second-set tiebreak 5-2 at one point before Durasovic clawed back and had set point at 7-6. Murray answered with three straight points to clinch the match.

READ MORE: Andy Murray and three others elected to ATP Player Council

American No 5 seed Taylor Fritz was a 6-4, 6-4 winner over Egor Gerasimov of Belarus. No 6 seed Alexander Bublik of Kazakhstan was less fortunate, retiring in his match against France's Arthur Rinderknech when Rinderknech was ahead 6-1, 2-0.

Spain's Pedro Martinez beat Finland's Emil Ruusuvuori 6-4, 3-6, 7-6 (4), and Botic Van de Zandschulp of the Netherlands squeaked by Nino Serdarusic of Croatia 7-6 (5), 7-6 (5).