With its regular referees locked out, the NBA is confident in its replacements – even the two it previously fired.

The NBA began preseason play Thursday night with 62 referees. The league said more than half have officiated in the NBA Development League, and all but five have worked the summer league.

It also said the two with NBA experience, Michael Henderson and Robbie Robinson, were some of the best replacements available.

Realizing the scrutiny the backups face, the league reminded teams Wednesday about its rules against publicly criticizing the officials. But senior vice president of referee operations Ron Johnson believes the teams won't have much to complain about.

"I think some people rise to the most amazing level of performance at amazing times," Johnson said. "So we'll see."

The league had the replacements in training camp last weekend, but thought it wouldn't need them. The NBA said the referees union agreed in principle on a new contract Friday, but backed out of the deal two days later. The league told teams Tuesday it was going ahead with the backups.