Padraig Harrington was leading the charge to catch US PGA Championship leader Tiger Woods as the World Number One defended a four shot overnight lead at Hazeltine National.
Woods got his third round under way at seven under par in Minnesota in the knowledge he had not lost the eight Major Championships he had led at the halfway stage.
The five man group four shots behind him, containing defending champion Harrington, US Open Championship winner Glover, England's Ross Fisher, Australian Brendan Jones and two-time winner Vijay Singh, had other ideas, as did Lee Westwood a shot further back at two under par.
Glover birdied the par four second to close the gap before four time US PGA champion Woods also birdied the hole to return his lead to four shots.
It was short lived, though, as Woods bogeyed the first par three at the fourth and Westwood moved within three after birdies at the second and seventh, only to then double bogey the par three eighth and fall back to two under.
Korea's Y E Yang also got to four under having started at one under as he went out in 33 and Harrington was the next to get there, the Irishman sinking a birdie at the seventh, putting from eight feet and then another at the eighth, from 18 feet, to move into outright second place at five under.
With another windy day in progress at the 7,674 yard layout near Minneapolis, the longest course in Major Championship history, there was also a threat of thunderstorms disrupting the leaders as they got their rounds going under overcast skies and there were signs Woods may have been off form following his bogey as he scrambled to save par at both the fifth and the sixth holes.
Glover joined Harrington at five under with a birdie at the seventh and Singh, having bogeyed the sixth, made his first move in the right direction with an eagle three on the seventh as Woods again worked hard to save par.
Denmark's Søren Kjeldsen, meanwhile, moved alongside Harrington and Glover with his third birdie in a row at the 11th, four under for his round.
The European challenge was further boosted by Players champion Henrik Stenson of Sweden and Northern Irishman Rory McIlroy, who all got to three under, as did South African Ernie Els.
Stenson recovered from an opening bogey to send down four birdies in his next eight holes and the Swede was three under after 12, as was McIlroy, who also bogeyed the first and then carded his fourth birdie of the day at the tenth.
Spain's Alvaro Quiros made amends for a second round 76 with a second 69 of the week to return to two under par but Fisher, playing with Harrington, was having less joy, bogeying the third and the fifth holes before his first birdie of the day came at the seventh.
Westwood's partner Ian Poulter had also started at two under but was one over par after nine holes but Graeme McDowell of Northern Ireland, who had led the tournament during the second round but fallen away for a 75, bounced back with a third round 71, level par for the week.