Home favourite Dantorp stole the spotlight from fellow Swede and world No 2 Henrik Stenson, who was playing the event for the first time since 2011, by firing a bogey-free 66, the same six-under score as Pepperell.
Stenson sat three shots behind following a 69 to leave him alongside Spanish veteran Miguel Angel Jimenez whose recent good form has catapulted him to the brink of Ryder Cup qualification at the age of 50.
Gallacher was in a tie for third place after an impressive opening 67 which included three birdies on the first four holes. A further birdie at the 11th was followed by his only bogey at the 12th, but the Bathgate man finished with a flourish with a pair of birdies on 17 and 18. His five-under-par round was matched by Daan Huizing of the Netherlands, Gareth Maybin of Northern Ireland and Swedes Rikard Karlberg and Sebastian Soderberg.
After five birdies and a bogey Stirling’s Lee was on four under par, a shot clear of a group including Stenson, Jimenez, fellow Scot Scott Jamieson and English duo Simon Dyson and Oliver Fisher.
Dantorp began his round on the back nine and birdied 11 and 12 before picking up further shots on 16 and 18 to reach the turn in 32.
More birdies followed on one and six to put the 25-year-old at the top of the leaderboard alongside Pepperell who birdied his final two holes to complete a 66 containing just a single dropped shot.
Stenson’s erratic 69 contained just seven pars as he began his campaign to avenge a painful play-off defeat to Mark Hensby in 2005.
Thomas Bjorn was on two under after an opening 70 while in-form Shane Lowry was a further shot back with Victor Dubuisson, Peter Hanson and Jonas Blixt amongst the later starters.
Scots trio David Drysdale, Jack Doherty and Chris Doak were level with Bjorn on 70, while compatriots Alastair Forsyth and Jamie McLeary, Paul Lawrie and Richie Ramsay were two shots further back after level par rounds of 72.