Del Potro, the No. 1 seed, dispatched Marinko Matosevic 6-2, 6-2 and will face Gilles Muller in Saturday's semifinal round. Muller defeated Paolo Lorenzi 6-3, 6-4 Friday.
Tipsarevic, seeded second, was leading Aljaz Bedene 6-2, 4-2 when Bedene retired. Tipsarevic will meet Grega Zemlja Saturday, following Zemlja's 6-4, 4-6, 6-2 quarterfinal upset of third-seeded Tommy Haas.