DOHA: Defending champion Novak Djokovic entered the Qatar ExxonMobil Open quarterfinal with a 6-3, 6-4 victory against Horacio Zeballos at the Khalifa International Complex here on Wednesday.
Djokovic next plays 38-year-old Radek Stepanek after the Czech knocked out Belgium's Arthur De Greef, 14 years his junior, 6-3, 6-2.
Also entering the round of eight is world No.1 Andy Murray who beat Gerald Melzer 7-6, (8-6) 7-5.
If the tournament goes to form, the pair will meet in their first clash of the season on Saturday.
Djokovic, the world No.2 won his second- round match 6-3, 6-4 in just 72 minutes, thanks to a break of the Argentinian's serve in each set.
But after the pair shook hands, Djokovic was taken by surprise, when Zeballos took a selfie on court.
"Making a selfie, that's the first time I have had this experience in my career," said the Serb. "Horacio -- well done, very original."
Earlier, Belgian fourth seed David Goffin, who beat Murray in an exhibition match in Abu Dhabi last week, lost 1-6, 6-7 (6-8) to Spain's Fernando Verdasco.
Andy Murray (GBR x1) bt Gerald Melzer (AUT) 7-6 (8/6), 7-5
Nicolas Almagro (ESP) bt Philipp Kohlschreiber (GER x7) 7-6 (7/5), 7-6 (8/6)
Fernando Verdasco (ESP) bt David Goffin (BEL x4) 6-1, 7-6 (8/6)
Radek Stepanek (CZE) bt Arthur De Greef (BEL) 6-3, 6-2
Novak Djokovic (SRB x2) bt Horacio Zeballos (ARG) 6-3, 6-4
Ivo Karlovic (CRO) bt Karen Khachanov (RUS) 7-6 (7/3), 7-6 (7/3)
Tomas Berdych (CZE x3) bt Jiri Vesely (CZE) 7-6 (7/5), 1-6, 6-1
Jo-Wilfried Tsonga (FRA) bt Dustin Brown (GER) 6-1, 6-3