Saints coach Nathan Brown, who revealed Meli's injury in the post-match press conference, admitted referee Richard Silverwood had no alternative but to show a red card to the former New Zealand international for a swinging arm on Rovers' two-try winger Craig Hall.
The sending-off came eight minutes before half-time with Saints trailing 12-6 and Brown believes it was a crucial factor in his side's first opening-round Cup exit for 18 years. "I don't think he had much choice," Brown said after his team's 26-18 loss.
"Franny's a very clean player - he's rarely penalised at all. It was just a reflex action and that can happen when you're out wide as an outside back defender when there's big spaces. It was a great effort to get to the front with 12 men. It was just unfortunate, with the incident that happened, that we couldn't hang on."
Saints had two players - Jon Wilkin and Ade Gardner - put on report for late tackles before being reduced to 12 men, and they paid the price for their indiscipline as Hull KR raced into a 12-0 lead thanks to tries from Hall and prop Mickey Paea.
Hall overcame the effects of the horrific-looking challenge from Meli to score his second try before half-time and, after Saints had edged in front courtesy of tries from Paul Wellens and Mark Percival, full-back Greg Eden clinched victory for the home side by scoring one try and creating another for centre Liam Salter.
"This club holds the Challenge Cup in pretty high standing and to get a win against a great side like St Helens is very pleasing," Rovers coach Craig Sandercock said.
"I was concerned when Saints got in front. That first 10 minutes after half-time we were very sloppy but there is some character in this team. The young kids rolled their sleeves up and in the end I thought we deserved to win."
Sandercock was also delighted with the impact made by Eden, who was signed by Brown during his time at Huddersfield and subsequently hailed by him as Britain's Billy Slater. Brown stood by his comments after watching him apply the finishing touches to his side's defeat.
He said: "Greg Eden is a brilliant young player, I've said that all long. He's a wonderfully gifted player. There are parts of his game he needs to be a little more consistent at, which he knows, but with experience and hard work he's going to develop. He's the type of player fans like to watch."