Juventus failed to win for the first time in 13 Serie A matches as lowly SPAL earned a 0-0 draw at Stadio Paolo Mazza on Saturday.
Heavily favoured to strengthen their grip on the Scudetto against the relegation-threatened Biancazzurri, Juve could instead have their lead trimmed back to two points on Sunday when Napoli host Genoa.
Alex Sandro's early blocked shot and a marginally misdirected Paulo Dybala free-kick were the best of few opportunities extracted from the plucky hosts.
SPAL had begun with the confidence of a team unbeaten in their previous three outings and richly deserved the point that moves them out of the bottom three.
Juve, conversely, looked heavy-legged in their fourth match in 11 days and struggled to produce anything that would cause concern Real Madrid, their Champions League quarter-final opponents.
Massimiliano Allegri's side did manage to equal their own Serie A record of 10 consecutive clean sheets – last achieved in 2015-16 – but it will be scant consolation as the door creaks open for Napoli.
Alex Sandro returned to the starting XI in an advanced role and the move almost paid off early, with only a sliding Filippo Costa denying him a clear sight of goal.
Gonzalo Higuain and Paulo Dybala soon tried their luck without success, while Daniele Rugani was capably managing SPAL's encouraging incursions.
Juve had scored twice by the 22nd minute in the last meeting between these teams, which ended 4-1 to the Turin club, but there was to be no early breakthrough on this occasion as the hosts held their shape beyond the half hour.
Kwadwo Asamoah sliced over the crossbar before a curling Dybala free-kick brushed the top of the net as the opening period edged to a close without the expected opener from a slightly off-colour Bianconeri.
Douglas Costa set a more enterprising tone after the restart with a firm left-footed effort that was palmed away by Alex Meret.
Dybala – overlooked by Jorge Sampaoli for the latest Argentina squad – next fired wide and, with scores still level by the hour, Allegri ushered Mario Mandzukic off the bench to replace Asamoah.
The visitors' command of possession passed 60 per cent amid their constant probing for the all-important winner, but they were frustrated in their attempts as a Mandzukic header in the 82nd minute failed to trouble Meret.
Instead, SPAL remained compact and held on for a precious point, just their fourth they have managed against Juve at Stadio Paolo Mazza since 1957.
Key Opta facts:
- Juventus failed to score for the first time since December (v Inter) in Serie A.
- Juve have equalled the record of 10 consecutive clean sheets in Serie A, established by the Bianconeri in March 2016.
- SPAL are now a streak of four Serie A games without a loss, which represents their best run of the season.