User blog comment:B214/Shin DxD 1 discussion/@comment-39.51.215.62-20180720122533/@comment-28884330-20180720165549

Ishibumi never said Issei would only lose one match. Ishibumi simply said he wanted Issei to lose a match and that was Dulio’s, but he never said that would be the only one he would lose. Saying so would be an immense spoiler.

However, you’re right he won’t lose against Rias. Considering how their teams stack up to each other’s, the only way for Rias to win without an asspull is for the Rating Game match’s ruleset to favor her or for Valerie to reveal some hidden ace or Balance Breaker, since she hasn’t had any spotlight.