The 27th-ranked player in the world, Coric saved nine of 12 break points while breaking Tsitsipas' serve three times in six opportunities. Despite the loss, Tsitsipas served 14 aces without a double fault.
Third seed Andrey Rublev of Russia also bowed out, with Grigor Dimitrov of Bulgaria prevailing 6-3, 6-4. American Marcos Giron also upset British seventh seed Cameron Norrie of Great Britain 6-3, 6-4.
No. 1 seed Daniil Medvedev of Russia had an easier time while defeating Dominic Thiem of Austria 6-3, 6-3. No. 5 seed Hubert Hurkacz of Poland outlasted Finland's Emil Ruusuvuori 7-5, 4-6, 6-3, and Italian sixth seed Jannik Sinner beat Francisco Cerundolo of Argentina 7-5, 6-3.
Swiss Indoors Basel
No. 3 seed Felix Auger-Aliassime of Canada needed just 49 minutes to defeat Serbia's Miomir Kecmanovic 6-1, 6-0 in the second round in Basel, Switzerland.
Auger-Aliassime had a 10-0 advantage in aces, never faced break point and won an overwhelming 22 of 24 first-service points (91.7 percent) in the rout.
No. 6 seed Roberto Bautista Agut knocked out Great Britain's Andy Murray 6-3, 6-2, despite Murray saving five of nine break points. Bautista Agut stayed in it by saving seven of eight break points.
Switzerland's Stan Wawrinka will face Bautista Agut in the quarterfinals after the three-time Grand Slam winner outlasted American Brandon Nakashima 6-4, 5-7, 6-4. Holger Rune of Denmark and Alexander Bublik of Kazakhstan also advanced.
