Loch, continuing the Germany tradition of outstanding performances in the sport, had a total time of 1:44.149 for his two trips down the Olympic course. The final two runs will be held Sunday.
Russian Albert Demchenko, who won the silver medal eight years ago, nipped Loch by .015 of a second on the first run. Loch then turned in a flawless second run to build a lead of .294 of a second over Demchenko going into Sunday's competition.
Armin Zoeggeler of Italy was third, .744 of a second behind the front-runner.
Germany has won the luge singles gold medal in five of the last seven Olympics. The only break from that trend has been provided by Zoeggeler, who won the event in both 2002 at Salt Lake City and 2006 at Turin.
Zoeggeler won the bronze medal in Vancouver.
David Moeller of Germany, silver medalist four years ago, was 14th midway through the competition.