GLASGOW, Jan 12 (Reuters) - Holders Celtic eased into the fifth round of the Scottish FA Cup with a 3-0 win over second division Stirling Albion on Saturday, when seven matches were postponed due to frozen pitches. Dutch striker Jan Vennegoor of Hesselink headed Celtic in front in the first half. Australian forward Scott McDonald added a second in the 70th minute before Japanese midfielder Shunsuke Nakamura fired a third to complete the scoring. Motherwell fought back for a 2-2 draw at Hearts thanks to a double from Chris Porter in their first match since the death of skipper Phil O'Donnell. Hibernian won 3-0 at home to Inverness Caledonian Thistle with a hat-trick from Dene Shiels in their first match under new Finnish manager Mixu Paatelainen and St Mirren beat fourth division Dumbarton 3-0. Second division Morton sprung a surprise when they drew 2-2 at home to Scottish Premier League side Gretna. Jim McAlister nabbed their late leveller in 75 minutes with a deflected 16-metre shot . Falkirk drew 2-2 with Aberdeen. Premier League clubs Dundee United and Kilmarnock both had their matches postponed while league leaders Rangers face fourth division East Stirling on Sunday.