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Denis Istomin upsets two-time MercedesCup runner-up Philipp Kohlschreiber in straight sets on Tuesday.

Read & Watch: Istomin Upsets Kohlschreiber In Stuttgart

Fucsovics, Simon also advance on rain-filled Tuesday in Stuttgart

Only three men advanced to the second round on a rain-interrupted Tuesday in Stuttgart, but that didn't stop an upset from occuring at the MercedesCup.

Denis Istomin snapped a seven-match losing streak at all levels to notch his first win at the event, defeating two-time runner-up Philipp Kohlschreiber 7-6(2), 7-6(3).

The World No. 100 won 77 per cent of service points en route to victory after one hour and 41 minutes in a match that featured no breaks of serve. The 31-year-old improves to 4-2 in his FedEx ATP Head2Head record against the German, who was bidding to record his 16th victory in 30 tour-level matches this season.

Istomin will face another German in the second round after Florian Mayer's victory over countryman Yannick Maden on Monday.

Banque Eric Sturdza Geneva Open champion Marton Fucsovics also advanced in straight sets, beating American qualifier Denis Kudla 6-3, 6-4. Fucsovics, who broke into the Top 50 of the ATP Rankings for the first time last month, dropped just two points behind his first serve throughout the 68-minute contest and saved all five break points he faced.

The Hungarian will meet No. 7 seed Milos Raonic or Diema Xtra Sofia Open champion Mirza Basic in the second round.

Watch Hot Shot: Kohlschreiber Floors Istomin

Gilles Simon dropped just three games to cruise past Italy's Matteo Viola 6-0, 6-3. The Frenchman converted six of eight break point opportunities to reach the second round after 70 minutes.

As a result of the poor weather in Stuttgart, Wednesday's order of play will provide fans with high-profile entertainment from the first ball to the last. Top seed Roger Federer makes his long-awaited return to the ATP World Tour, while defending champion Lucas Pouille, #NextGenATP Canadian Denis Shapovalov, 2016 Wimbledon finalist Milos Raonic and 2017 Fever-Tree Championships winner Feliciano Lopez are also in action.

Did You Know?
Philipp Kohlschreiber falls to 16-12 at the MercedesCup after his loss to Denis Istomin on Tuesday. The German was making his 13th appearance at the tournament, where he has reached the championship match on two occasions. Kohlschreiber led both finals he played, before falling in three sets to Fabio Fognini in 2013 and Dominic Thiem in 2016.

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