Välimäki and Garcia-Heredia were among the earlier starters and their mark of ten under was regularly threatened but by the end of the day only Rozner had caught up with them.
Oliver Bekker managed a 71 to sit one back, a shot ahead of Christoffer Bring, Casey Jarvis and Pierre Pineau.
Välimäki shot a course-record 62 on Thursday and, after starting his second round at the tenth, hinted that another low round was coming with birdies at the 11th, 14th and 15th but a first dropped shot of the week arrived at the 16th and he bogeyed the second as well.
He struck back at the next with a birdie but a bogey-double bogey finish, after a birdie at the seventh, sent him to the clubhouse to sign for a level-par 72.
Garcia-Heredia began at the tenth too and he birdied three in a row from the 12th, picked up another shot at the 18th and three more at the fourth, fifth and seventh. His only bogey of the day in his 66 came at the difficult eighth.
"It was fun out there today," said Garcia-Heredia. When asked what areas of his game were strong he said: "All of them. I played really solid yesterday and really solid today. I improved my putting. I went to see a putting coach because last year wasn't very good. I'm really happy with all of that."
Rozner appeared to be heading for the top of the leaderboard on his own.
The Frenchman went into the second round eight shots off the pace and made steady progress on his front nine before bursting into life on the way home.
He fired four birdies on the way out before four in a row from the 12th took him alongside Välimäki and Garcia-Heredia.
He gave himself a look at another birdie at the 16th with a fine approach after missing the fairway with his tee shot but this time the putt just stayed out.
There was still the par-five 18th to come but a birdie was always going to be a big ask after he was short and left with his second.
In the end he had to work hard for the par that enabled him to card a bogey-free 64.
He said: "I think it's one of the first times in my career I'm happy with every single score on every single hole. That doesn't happen a lot and I don't think I can score any better on this course. It was tricky, it was tough so I'm really pleased with the way I played.
"You had to aim so far right or so far left in the side winds. I made one mistake on five but after that I didn't make a lot of mistakes. But putting was solid, short game as well so I'm happy with everything."
Rozner's countryman Pierre Pineau looked like being the man to catch when he recovered from an opening bogey at the tenth with a run of five birdies from the 11th.
But he dropped a shot at the 16th and found reverse with three bogeys on the spin from the second.