Stefanos Tsitsipas reached his fourth Australian Open semi-final as the Greek defeated Czech Jiri Lehka 6-3 7-6 (2) 6-4 on Tuesday.
The third seed dominated after breaking a nervous Lahika in the opening set but was then pushed hard against the 21-year-old who enjoyed a breakout tournament.
Lahika, who had never won a Grand Slam match before arriving in Melbourne, used her powerful baseline game to stay with Tsassipas in the second set but the Greek stepped up to ease through the tiebreak.
Tsitsipas was forced to save three break points in a row at 3-3 in the third set as Lehecka threatened to extend the Rod Laver Arena clash.
The 24-year-old then served with Lahika at 4-5, reached match point with a backhand pass and sealed victory as her opponent netted a backhand.
Tsippas will face Russian Karen Khachanov in the semi-finals.