Loeb has two races left to overtake Gronholm in the standings

The Finn set a time of 1:30.8 around the grounds of Stormont Buildings with Citroen's Loeb close behind on 1:31.7.

Northern Ireland driver Kris Meeke lies third with a time of 1:31.8 ahead of Friday's nine special stages.

Ford driver Gronholm leads Loeb by four points with just the Rally of Great Britain to follow the Irish round.

Dungannon man Meeke got the four-day event underway in his Subaru Impreza and his time proved difficult to beat until the world's top two took to the track.

606: DEBATE Give your thoughts on this week's Rally Ireland

Australia's Chris Atkinson, Norwegian Petter Solberg, Finns Mikko Hirvonen and Jari-Matti Latvala and Spaniard Daniel Sordo completed the top eight.

A crowd of 11,500 packed into the Stormont grounds to watch the opening showpiece.

The action continues from the rally's base in Sligo on Friday morning at 0800 GMT with the event taking in both sides of the border and comprising 20 stages over three days.

Loeb, from France, is seeking his fourth consecutive world title and should he fail to finish, as he has three times this season, Gronholm will only need to finish second in the inaugural Irish WRC event to claim his own third title.

Rally Ireland positions after Thursday's super-special stage in Belfast
1st Marcus Gronholm (Finland, Ford Focus) 1:30.8
2nd Sebastien Loeb (France, Citroen C4) 1:31.7
3rd Kris Meeke (Northern Ireland, Subaru Impreza) 1:31.8
4th Chris Atkinson (Australia, Subaru Impreza) 1: 32.0
5th Petter Solberg (Norway, Subaru Impeza) 1:32.2
6th Mikko Hirvonen (Finland, Ford Focus) 1: 32.5
7th Jari-Matti Latvala (Finland, Ford Focus) 1:32.5
8th Daniel Sordo (Spain, Citroen C4) 1:32.7