Juho Hanninen took the lead from Andreas Mikkelsen on the only Circuit of Ireland night stage that took place before an early halt was called to Friday's action.
The field had been scheduled to make second passes through both Drummond and Legane after dark, but only the former stage ran as delays mounting up from earlier in the evening convinced the organizers to call off SS5.
Before then, Hanninen (Skoda) went quickest in changeable weather on SS4, inching into an overall lead of just 0.6 seconds over Mikkelsen (Skoda UK) going into Saturday's three loops of stages.
Jan Kopecky remains third in the other factory Skoda, with Alastair Fisher jumping to fourth in his Ford after set-up changes in service helped him to a rapid time on Drummond.
The World Rally Championship Academy leader vaulted Mathieu Arzeno to take the place. The Frenchman's Sainteloc Peugeot team-mate Craig Breen is back in seventh, behind Robert Barrable's Skoda, after penalties for being late into service following a road section fuel pump problem were applied.
Leading positions after SS4:
Pos Driver Team/Car Time/Gap
1. Juho Hanninen Skoda 34m55.7s
2. Andreas Mikkelsen Skoda UK + 0.6s
3. Jan Kopecky Skoda + 28.2s
4. Alastair Fisher M-Sport Ford + 48.4s
5. Mathieu Arzeno Sainteloc Peugeot + 1m02.4s
6. Robert Barrable CA1 Skoda + 1m18.5s
7. Craig Breen Sainteloc Peugeot + 2m27.0s
8. Sepp Wiegand Skoda Deutschland + 2m34.4s
9. Garry Jennings Mitsubishi + 2m44.0s
10. Sam Moffett Mitsubishi + 2m53.1s