Isaac Price's hat-trick powered Northern Ireland to a stunning 5-0 win over Bulgaria that sent them top of their Nations League group.After battering Belarus without reward in the opening 45 minutes of Saturday’s goalless draw, Northern Ireland took their frustrations out on Bulgaria as Price became the first Northern Ireland player to hit a treble since David Healy in a 4-1 win over Liechtenstein in March 2007.After the Standard Liege forward got the opening two, Brodie Spencer’s shot hit a post and rebounded in off Bulgaria goalkeeper Dimitar Mitov to make it 3-0 at the break.Price completed his hat-trick with the best goal of the night, a rising shot from the edge of the box, before Josh Magennis came off the bench to hit a late fifth.The last time Northern Ireland won 5-0 at home, George Best scored a hat-trick against Cyprus in April 1971.With Belarus and Luxembourg drawing 1-1 in Hungary, Northern Ireland sit top of League C Group 3 by one point before facing those two teams in their final games next month.Bulgaria arrived in Belfast unbeaten in nine games under manager Ilian Iliev, including a 1-0 win over Northern Ireland in Plovdiv last month, but that came to a sudden halt as Michael O’Neill’s men made it four wins in their last five at Windsor Park.Group rivals Luxembourg registered their second successive point after a 1-1 draw in Belarus.Scotland secured their first Nations League point with a gutsy goalless draw against Portugal at Hampden Park.Much of the interest centred on the visitors' striker Cristiano Ronaldo whose every involvement brought boos, jeers or cheers from the Tartan Army.And while Roberto Martinez’s side, who arrived top of League A Group 1 with nine points from nine, dominated the ball,