Zheng Qinwen makes big US Open comeback. Naomi Osaka joins her in the fourth round

NEW YORK – Zheng Qinwen was on her back with her arms in the air, celebrating a U.S. Open victory maybe only she believed was possible.

Madison Keys fought off tears as she tried to explain how Zheng, way down and all but out, somehow got the win.

Zheng, the Olympic gold medalist, extended her return to the U.S. Open on Saturday with a spectacular and stunning rally, winning the final seven games to eliminate No. 22 Keys 1-6, 7-6 (3), 7-5.

“I feel like I obviously got off to a really good lead, and then I just got really — I mean, got…