If Pablo Carreno Busta loses his second-round match in Vienna on Friday against Del Potro's fellow Argentine Diego Schwartzman, the South American would move into the eighth and final qualifying spot for the year-end tournament. "I'm exhausted, but I'm still winning and playing good tennis", the world number 19 said. "I've been playing a lot of matches".
Fourth-seeded Del Potro needed exactly two hours to win 6-2, 2-6, 6-4 against sixth-seeded Roberto Bautista Agut of Spain.
"I played better than yesterday, but tomorrow I need to improve a little bit more".
"I will be ready for Saturday, it will be a challenge for me, I'm glad to reach the semi-finals of this event again".
He next faces Julien Benneteau of France, who saw off American Donald Young 6-4, 6-2.