GLASGOW, April 5 (Reuters) - Simon Lappin lashed in a first-half winner for 10-man Motherwell to dent champions Celtic's title hopes in a 1-0 victory in the Scottish Premier League (SPL) on Saturday. Motherwell's former Rangers defender Bob Malcolm was sent off in 51 minutes for a foul on Italian midfielder Massimo Donati. Hibernian beat St Mirren after going 2-0 up in the first five minutes with goals from Colin Nish and Moroccan Merouane Zemmama. Kilmarnock and Hearts drew 0-0 while Gretna lost 2-1 to Inverness Caledonian Thistle. Leaders Rangers, with 74 points from 29 games, face Dundee United on Sunday and can stretch their lead further with Celtic now on 68 from 31.