Local favorite Miguel Angel Jimenez, a four-time winner on the European Tour this season, fired a 63 to join Darren Fichardt and Johan Edfors in a tie for second at 9-under-par 133. Graeme McDowell, Anders Hansen and Gary Murphy followed at 8-under-par 134.
Broadhurst, whose last victory came at the 1995 Open de France, started on the back side at Club de Campo and picked up his first birdie of the day at the par-3 11th. Broadhurst then birdied the par-5 14th and hit his second shot to 3 feet for a birdie at the par-4 18th.
The Englishman continued his fine play on the front half with a birdie at the par-4 second after his approach stopped within 8 feet of the hole. Broadhurst made it two in a row with a birdie at the third and looked to be in trouble at the sixth, but drained a 10-foot putt to save par.
Broadhurst birdied the seventh before finding trouble with a bogey at the par-4 eighth, his first dropped shot of the tournament. The 39-year-old recovered with a birdie at the par-3 ninth, his last, to secure the outright lead heading into the weekend.
'I got back to where I should be. It'd be nice to finish the season off with a win,' said Broadhurst. 'The last couple of weeks I've just started to enjoy it a little bit. Not put too much pressure on myself.'
While Broadhurst was enjoying the lead in the clubhouse, Jimenez was gaining momentum on the back nine and nearly grabbed a share of first. After a trio of birdies on the front side, Jimenez tallied a birdie at the 12th and hit his second shot within inches of the hole for a tap-in birdie at the 13th.
Jimenez made it three straight with a birdie at the 14th and ran off back-to-back birdies starting at the 16th to reach 9 under. Jimenez had a long birdie chance at the last, but missed left before tapping in for a closing par.
Edfors is in danger of losing his card, but a victory this week would remedy his situation. The Swede collected a pair of birdies and an eagle of his first nine holes to make the turn at minus-9.
Edfors struggled with bogeys at the 10th and the 11th, but was able to get a shot back with a birdie at the 13th. He added a birdie at the 17th to complete a round of 67.
Fichardt played the back side first and tallied a lone birdie at the 13th. The South African caught fire around the turn with four consecutive birdies starting at the par-4 first and grabbed a piece of the lead with a birdie at the seventh. Fichardt stumbled to a bogey at the ninth, however, to finish one back after a 66.
Trevor Immelman, Brett Rumford, Richard Sterne, Jamie Donaldson and Jose Manuel Lara shared eighth place at 7-under-par 135.
The 36-hole cut fell at 1-under-par 141 with 80 players qualifying for the weekend, including defending champion Ricardo Gonzalez, who made the cut on the number.