But the elusive additional birdie he needed to take the outright lead would not drop and he would eventually bogey the last to fall into a group of ten at 5 under.
Rumford, who now has virtually no status on the European Tour as such, is obviously happy with his start but was relatively circumspect in his assessment of his play.
He has won four events on the European Tour, the last of those in 2013, but he has been plagued by health issues and a subsequent loss of form in recent years.
ROUND ONE HIGHLIGHTS PERTH SUPER 6:
“It was really nice, just a solid 33 front, 33 back, for a 66, that's pretty much how the round unfolded,” he said after his round.
“It was nothing ‑‑ no stretches of brilliance, just a consistent round of golf, controlled the ball pretty much how I wanted it most the day and, yeah, I think the golf course is set up that way as well.”
For Rumford this start opens up the possibility of a hometown win for him but he is not getting ahead of himself.
“I'm just taking it one tournament at a time,” he said. “I can't look ahead at all because I'm really not too sure which events I'll be getting in.
“I know there's a few key events in which being in the winner’s category that I will be focusing all my attention around.
“So, I'm prepping for China, Irish Open, and then the Omega, European Masters, I know I'm definite for those (he has won those events before) so they're definitely a priority. Every week is pretty much a priority for me at the moment so am taking every week, that opportunity to go win a tournament.
42 year-old Foster has won only once on the European Tour, that coming back in 2003, and his most recent form hardly gave an indication that such a good opening round was in store this week.
His round included seven birdies and just the one bogey coming at his 9th hole.
Tanihara, the runner-up on the Japan Tour’s money list last year, is a fourteen-time winner on the Japan Tour and the runner-up in last year’s New Zealand Open.
He was no doubt disappointed with a dropped shot at the last but he is an immense talent and could continue to play a role as the week goes on.
“I'm really happy and satisfied," said Tanihara through an interpreter after his round. “My first goal is to play until Sunday, hopefully get to Sunday.
“And playing in a match where there's only six holes it's different and really looking forward to playing that match.
"The goal is to get to the top 50 which get into The Masters and I’m 58 in the world right now, so try to get as much in tournaments, play well, points, and just do my best."
Pre-tournament favourites, Louis Oosthuizen and Alex Noren, began with rounds of 69 and 74 respectively leaving the leading world ranked player, Noren, with a lot of work to do over the next two rounds.