Frenchman Jean-Francois Lucquin shot a 5-under 67 to join Scotland's Andrew Coltart in a share of third place at 2-under-par 142. Coltart fired a 6-under 66 Friday to establish a new course record at Ballyliffin.
Gusting winds that greeted the players Thursday were significantly down during Friday's round, making scores lower.
Rocca, the winner of the inaugural North West of Ireland Open in 1999 at Galway Bay , birdied 11 and 13 to match Florioli in the lead at 3-under par. Rocca drained a 35-foot birdie putt at the 17th to take sole possession of the lead.
'I didn't putt very well today,' said Rocca, who was part of a five-way tie for first after Thursday's first round. 'Just holed a good putt on the 17th. But I missed quite a few chances.'
Rocca's last victory on the European Tour was at Galway in 1999 and the 45-year-old last owned a 36-hole lead on tour at the 1996 European Open.
'Leading is a nice place to be in,' said Rocca, who defeated a young Tiger Woods in the Sunday singles at the 1997 Ryder Cup. 'I don't think about the weekend. Just think about the way I am swinging now and keep my rhythm and try to make more birdies.'
Florioli broke out with two birdies in his first three holes and recorded another at 10 to get to 4-under par. He dropped shots at 13 and 15 to fall back into the pack but got one back when he birdied the par-4 16th for the second time in as many days.
'The weather was much better today,' said Florioli, who is playing in his third event on the European Tour this season. 'I made a couple of mistakes like on the 13th, bogeyed that for the second day running, but overall very pleased. I holed a long putt on the first and that got me off to a good start with a birdie.'
Coltart was flawless Friday with six birdies and no bogeys and the former Ryder Cupper is now in contention for his first title of 2002.
'I played well and didn't do anything wrong,' said Coltart, who currently ranks 76th on the Order of Merit. 'It was nice to go out and make a significant move out there and get really involved in the tournament.'
Allan Hogh and Jesus Maria Arruti, who were part of a group tied for the lead following Thursday's first round, shot matching 72s Friday to share fifth at minus one.
England's Mark Sanders and a pair of Swedes, Anders Forsbrand and Adam Mednick, are tied for seventh at even-par 144.
The 36-hole cut fell at 7-over-par 151 and 89 players advanced to the weekend.
Full-field scores from North West of Ireland Open