Manchester City midfielder Martin Petrov did the damage when he broke through on goal after 38 minutes, although it was defender Jonny Evans who had the final touch in a desperate attempt to clear.
Northern Ireland’s best chances fell to David Healy but the North’s most celebrated goalscorer was unable to add to his international tally of 33. It was his country’s first defeat on home soil in seven matches.
Bulgaria, ranked 18th in the world, were the better team but Worthington was encouraged by competing throughout and also keeping Tottenham’s €40million-rated star striker Dimitar Berbatov quiet.
Meanwhile, John Toshack’s youthful Wales side recorded a confident victory over Norway at the Racecourse Ground in Wrexham.
Victory over a side who failed to qualify for Euro 2008 by just one point three months ago will give Toshack all the encouragement he needs as the World Cup qualifiers approach.
Wales took the lead with a goal from 27-year-old Carl Fletcher – and the Crystal Palace man ended as captain when Simon Davies was substituted.
But the Welsh side became younger as substitutes were introduced – and an outstanding second-half display by Jason Koumas, who scored the second and third on his hometown ground, just underlined Wales superiority.
Wales have now lost just two of their last 11 games, and their young players are growing in confidence and maturity in front of Toshack’s eyes.
Elsewhere, an outstanding Italy — top seeds in Ireland’s Group 8 — won a battle of European heavyweights against Portugal in an international friendly in Zurich on last night.
Luca Toni opened the scoring on the stroke of half-time before Andrea Pirlo made it 2-0 shortly after the restart.
Ricardo Quaresma reduced the deficit in the 77th minute before substitute Fabio Quagliarella made it 3-1 two minutes later.
The Azzurri are looking to follow up their World Cup triumph with a title at Euro 2008 and on this evidence Roberto Donadoni’s side will be one of the favourites.
Liverpool striker Fernando Torres lasted just 23 minutes of Spain’s 1-0 friendly victory over France before being forced off with what appeared to be a hamstring injury.
Although the 23-year-old went off in some discomfort it was not immediately obvious when Torres sustained the problem.
Liverpool, who play Chelsea in the Premier League this weekend, will be keeping their fingers crossed that the injury to Torres — their top scorer with 18 goals in all competitions — is not serious.
Joan Capdevila scored the winning goal for Spain with eight minutes to go although Thierry Henry was a constant threat and had a shot tipped round the post in the final minute.
Three second-half goals secured a comfortable win for Germany over Euro 2008 group-stage opponents Austria in Vienna.
Neither side could find the breakthrough in the first period but Thomas Hitzlsperger, Miroslav Klose and Mario Gomez were on target after the interval to give the visitors a convincing triumph over their neighbours.
Holland humbled Croatia in front of their own fans in Split with a comprehensive victory.
Johnny Hetinga’s early goal set Marco Van Basten’s side on their way, with Klaas-Jan Huntelaar doubling their advantage before half-time.
And Celtic striker Jan Vennegoor of Hesselink rounded off a good night’s work for the Dutch late on.
A 58th-minute goal by defender Nikolce Novevski earned Macedonia a 1-1 home draw with neighbours Serbia after Danko Lazovic had fired the visitors ahead.