Best was included in the starting line-up named on Wednesday, but has been receiving intensive treatment on the shoulder injury sustained during Sunday's victory over Italy.
"Rory's come up great and is fine to start the game," said defence coach Les Kiss.
Best sprained the AC joint on his right shoulder at Otago Stadium and was locked in a race against time to prove his fitness for Ireland's attempt to reach the semi-finals for the first time.
"We obviously had some precautions in place ready to cover him if he failed to pull through, but he's in tip-top shape so full credit to him and the medics," added Kiss.
Best's outstanding form as part of a highly-impressive Ireland front row compelled coach Declan Kidney to do everything possible to ensure his inclusion.
Number eight Jamie Heaslip is delighted the Ulster front row has been passed fit.
"It's great Rory's available because he's one of the senior players in the team," said Heaslip.
"He's an influential player and his darts in open play are great."
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