Stefanos Tsitsipas cruised into the quarter-finals of the Sydney International with a straight-sets defeat of Guido Andreozzi, while Taylor Fritz upset John Isner at the Auckland Open on Wednesday.

There are high hopes that Tsitsipas can kick on this year after winning the Next Gen ATP Finals in November and the top seed was too good for Andreozzi, winning 6-3 6-4.

Andreozzi was broken three times and, despite showing character to win three games in a row from 5-1 down in the second set, the lucky loser was unable to take it the distance.

World number 15 Tsitsipas will now come up against Andreas Seppi following the Italian's 7-6 (7-2) 6-2 triumph over Martin Klizan.

Alex de Minaur, runner-up in his homeland last year, advanced with a 6-4 7-6 (7-5) victory over American qualifier Reilly Opelka, setting up an all-Australian clash with Jordan Thompson.

Third seed Diego Schwartzman coasted to a 6-2 6-3 win over Guillermo Garcia-Lopez, while John Millman took out seventh seed Marton Fucsovics 6-3 6-4.

Yoshihito Nishioka and Gilles Simon progressed at the expense of Andrey Rublev and Sam Querrey respectively. 

Fritz claimed the scalp of world number 10 and fellow American Isner, winning 7-6 (7-3) 7-6 (7-5) to reach the quarter-finals in New Zealand.

Top seed Isner served 26 aces, but mini-breaks in each tie-break saw 21-year-old Fritz through. 

Fabio Fognini battled his way past Peter Gojowczyk, the third seed from Italy winning 6-2 3-6 7-6 (7-5).

Marco Cecchinato, the third seed, bowed out with a 6-3 6-3 loss to Tennys Sandgren, while Pablo Carreno Busta, Jan-Lennard Struff, Leonardo Mayer, Philipp Kohlschreiber and Cameron Norrie were the other winners on day three.