Filip Krajinovic dumped fifth seed Andrey Rublev out of the Kremlin Cup in his home city and David Ferrer came from a set down to avoid a shock first-round exit against Stefano Travaglia in the European Open on Tuesday.
Rublev became the second player to qualify for the Next Gen ATP Finals on Tuesday, but the 19-year-old was brought back down to earth by a 7-5 7-6 (8-6) loss to qualifier Krajinovic in Moscow.
Krajinovic is ranked 42 places below Rublev, but served 15 aces and claimed the only break in the first set to move into round two.
Seventh seed Paolo Lorenzi also made an early exit, Laslo Djere saving a match point in the second set before going on to win 4-6 7-6 (11-9) 6-4.
Sixth seed Damir Dzumhur, Lukas Rosol, Rogerio Dutra Silva, Andreas Seppi and Ricardas Berankis all advanced to round two.
Ferrer avoided a shock loss on day two in Antwerp, seeing off plucky Italian Travaglia 4-6 6-4 7-6 (7-3).
The fifth seed from Spain, playing his first match since losing to Mikhail Kukushkin in the first round of the US Open, dug himself out of a hole to advance after he was broken three times by the qualifier.
Seeded trio Pablo Cuevas, Benoit Paire and Alexandr Dolgopolov were beaten in the first round by Stefanos Tsitsipas, Joao Sousa and Henri Laaksonen respectively.
None of the seeds in action in the first round of the Stockholm Open suffered first-round losses, as Fabio Fognini brushed aside Malek Jaziri 7-5 6-1.
Yuichi Sugita came through a tussle with Denis Istomin 1-6 6-3 7-6 (7-4) after being 4-2 down in the tie-break, while Fernando Verdasco cruised to a 6-3 6-1 success over Robin Haase in the Swedish capital.
