Thiem rallies from a set down to defeat John Isner to set up a semifinal match against Alexander Zverev in Madrid Open.
The Spaniard eases past the Aussie in straight sets to enter the last-8 in Madrid Open for the 15th time.
Meanwhile, Hugo Nys and Tim Puetz bag their maiden ATP Tour team title at the Millennium Estoril Open.
The Czech star continues her fine 2021 form, beating World No.2 Osaka in three sets.
The three-time champion Kvitova edges past the German to reach the third round in Madrid.
Pliskova rallied from a set down to beat Gauff; No.11 seed Jennifer Brady had it easy against Venus Williams.
The Belarusian came from a set down to defeat the German favourite in a three-set thriller to set up a semifinal clash against Jan-Lennard Struff.
Meanwhile, Wesley Koolhof and Kevin Krawietz advanced to the BMW Open final in Munich.
Djokovic, who has only played four tournaments this year, suffered a surprise defeat to Aslan Karatsev in semifinals of the Serbia Open last week
Rafael Nadal defeated Stefanos Tsitsipas 6-4, 6-7(6), 7-5 on Sunday to win the Barcelona Open for a record-extending 12th time.