Cao, who reached the last 16 at the Crucible last April, led 4-1 after a top break of 70 before Tian won the next four frames with high scores of 73, 78 and 56.
But Cao recovered to make it 5-5 then won a tense decider by potting the final blue, pink and black. He now faces Matthew Selt and needs two more wins to reach the final stages in Chengdu in October.
Anthony McGill came from 3-1 down to beat Martin O'Donnell 6-4, firing in runs of 120, 114, 77 and 66.
India's two pros continued to shine as Pankaj Advani came from 4-1 down to beat Steve Davis 6-5 while Aditya Mehta closed with a 97 in a 6-3 win over Mike Dunn.
Norway's Kurt Maflin scored his second consecutive 6-5 win, making a vital 47 clearance in the decider to edge out Rod Lawler.
Thepchaiya Un-Nooh beat fellow Thai James Wattana 6-5 on the final pink while Belgian prodigy Luca Brecel saw off Jimmy Robertson 6-2 with a top break of 77.
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