The Scottish pair both posted seven-under-par cards - Forsyth had a 64 on the West Course and Lee a 65 on the East Course - and are joined in a four-way tie at the top with the South African Justin Walters and Italy's Edoardo Molinari.
In addition to the €206,000 first prize on offer, the opportunity to earn a place in July's Open Championship is a major incentive here.
The leading three players in the top 10 of the final leaderboard who are not already exempt into the Hoylake event, will earn an Open tee-time as part of the Royal & Ancient's new qualifying series.
The format has replaced the 36-hole international final qualifiers of past years. "You don't really change your strategy but it's a great reward for three lucky guys who'll get a chance to play in the Open," said Lee, who led last month's Abu Dhabi Championship with one round to play but slipped back to finish in a share of 10th.
"It's nice to have qualifiers throughout the year and not just geared up to that 36-hole sprint that most qualifiers are. Hopefully we can keep our games up and take one of those spots."
The last time Forsyth shot a 64 on the European Tour was in the first round of the Joburg Open in 2010. He followed it up with a 76 and missed the cut. Yesterday, he exploded out of the blocks to cover the front nine in just 30 shots. The inward half was less productive but his seventh birdie of the day, at the 15th, lifted him to the summit.
"The front nine was probably as good as I've played in a long time," said the 38-year-old, who is looking for his third European Tour title. "I seemed to do everything right on the front nine but struggled a little on the back, where I ended up between clubs a few times. But no dropped shots and seven birdies - I'm never going to complain with that."
Scott Jamieson had a 67 on the West Course and his fellow Glasgow man Marc Warren a level-par 72 on the East Course.
Meanwhile, in Portugal, Robert Arnott, a stalwart of the domestic Tartan Tour for more than a quarter of a century, earned a conditional card for the European Senior Tour after sharing 11th place in the qualifying school final last night.
The Bishopbriggs veteran, a former PGA Cup player, held his nerve after a potentially calamitous double-bogey on the 14th and birdied the next before making par on each of the last three to qualify on the two-over 286 limit. The top six, headed by England's Andrew Murray on 276, all earned full cards for 2014. The next eight, including Arnott, will have a more limited category.