Tidland, seeking his first Nationwide Tour win, collected six birdies against just one bogey to move into the lead at 13-under-par 200.
Lunde, who entered the third round with a two-shot cushion, stumbled to a pair of late bogeys and shot a 2-under 69 to join Tidland on top of the leaderboard.
They held a two-shot advantage on four players: Michael Putnam (66), Hunter Haas (66), Wade Ormsby (68) and Spencer Levin (69).
Matt Bettencourt (66) and Tag Ridings (70) were another stroke further back at 10-under 203.
Tidland made his run Saturday during a seven-hole stretch on the front nine when he made four birdies and a bogey on the way to posting an outward 33. But he didn't earn a share of the lead until rolling in a six-foot birdie putt at the 14th hole.
Posting another birdie at the 16th, Tidland moved into good position to pick up his first career Nationwide Tour win ' although he already owns a title on the Canadian Tour, won 10 years ago.
'It's an important week,' said Tidland, 35, who is hoping to get inside the top 25 on the money list to earn a PGA TOUR card for next season. 'It's coming down to crunch time. It hasn't been a good year but you're only a week or two away from a good year. A win would certainly turn things around.'
Lunde, after shooting a flawless 65 on Friday, was bogey-free through 11 holes of his third round before he dropped consecutive shots at the 12th and 13th holes. He rebounded with a birdie at the 15th to earn his place with Tidland at the top of the leaderboard.
The 32-year-old Californian claimed his only win at the Nationwide Children's Hospital Invitational in July.
'It hasn't been that I've had 50 birdie opportunities and I've made half of them,' Lunde said. 'The ones I've been able to make are the good 10- to 15- footers that I've had a chance to make.'