John Isner's hopes of qualifying for the ATP Finals were hindered by a three-sets defeat to Ernests Gulbis in the Stockholm Open semifinals.

Top seed Isner battled past American compatriot Tennys Sandgren on Friday to secure a win that moved him above Kei Nishikori into ninth in the ATP Finals rankings.

But his ambitions of gaining further ground on eighth-ranked Dominic Thiem were rocked by a 1-6 6-3 6-3 loss to Gulbis.

Former top-10 player Gulbis consequently reached a first ATP World Tour final since 2014, with Next Gen star Stefanos Tsitsipas standing in his way of glory.

Third seed Tsitsipas defeated Fabio Fognini (2), who himself remains an outside shot for the ATP Finals, in a one-sided 6-3 6-2 victory.

At the Kremlin Cup, Adrian Mannarino defeated Andreas Seppi 7-5 7-5 to set up a showpiece with Karen Khachanov, who defeated Daniil Medvedev 6-1 6-7 (5-7) 6-3 in an all-Russian semifinal.

Diego Schwartzman sustained more European Open heartbreak. The Argentinian, twice a runner-up in Belgium, lost out 6-3 6-4 to Gael Monfils.

That win for Monfils booked a final against top seed Kyle Edmund, who defeated 2016 champion Richard Gasquet 6-3 6-4.

It marks the second time Edmund has reached at ATP final, the first ending in defeat to Pablo Andujar in Marrakech in April.