Celtic secured a 10th successive victory, a Scottish Premier League record, at Tynecastle yesterday but yet again the champions pushed their luck.
It has all the hallmarks of a title run, but in truth Martin O'Neill's side have stumbled from game to game as they approach yet another Old Firm encounter with Rangers next Sunday.
At least this time they eschewed their recent habit of waiting until stoppage time to decide the issue. Henrik Larsson's 42nd-minute penalty was enough to grind out another three points. How he must love Hearts; this was the 15th time in four years that he had found the net against them.
Tynecastle has been filled with rancour for much of the last year with the sale of the club's Scotland internationals Gary Naysmith and Colin Cameron, but even that has failed to stem the red ink. On Monday, chief executive Chris Robinson had to announce a second successive loss of £4m to hostile fans and shareholders.
In the new, frugal era Hearts must rely on promising teen-agers from their youth system, such as Stephen Simmons, and budget buys, in the shape of Ricardo Fuller. The pair combined after just seven minutes when Simmons floated a delightful ball in behind the Celtic defence and Fuller got in before goalkeeper Robert Douglas, but the Jamaican international's volley skewed wide.
Celtic, in contrast, are spoilt for choice. John Hartson and Shaun Maloney hit six goals between them in the last outing, the 8-0 League Cup rout of Stirling Albion, but neither got further than the bench for this one, with Larsson and Chris Sutton restored to their usual partnership.
The pair's telepathy saw Larsson profit from Sutton's lay-off after the Swede dummied the original pass, but on each occasion Steven Pressley's reading of the situation rescued Hearts.
Yet it was the Edinburgh club who carved out the clearest chance when Alan Maybury earned a free-kick which was never dealt with properly by Douglas's defence. When the former Leeds United defender swept the ball back in, Kevin McKenna's hook shot arced over Douglas, whose fingertips just pushed the ball over the bar.
However, the deadlock was broken three minutes before the interval when Andy Webster, Hearts' young central defender, rashly scythed down Didier Agathe in the box. Larsson thrashed the penalty past Antti Niemi for his 13th goal of the season.
Any notion that the goal would open up the game was quickly dispelled in the second half, which was even tighter and more physical than the first. Space was at a premium and few players were afforded the time to get the ball down.
One of the few openings came when Fuller muscled his way to the edge of the box only to be abruptly halted by Mjallby, but McKenna's free-kick was charged down. Celtic never really had control of the game but it was another 20 minutes before Douglas was called on to touch Maybury's inswinging corner over.
Niemi then defied Mjallby's burst into the box before Douglas produced a vital stop with 12 minutes left as he dived to push out Fuller's header from Steve Fulton's corner in a torrid finale.
Heart of Midlothian 0 Celtic 1
Larsson pen 44
Half-time 0-1 Attendance: 15,570Reuse content