Sunderland again proved a scourge for Chelsea when holding the Premier League leaders to a 0-0 draw at the Stadium of Light on Saturday.
Jose Mourinho's men had scored in every league match this season, yet could not find a way through against the team who handed them their last domestic defeat.
The pre-match expectation was for Chelsea, six points clear of their nearest challengers at kick-off, to collect an 11th win from 13 league outings.
Yet Sunderland, who triumphed 2-1 at Stamford Bridge in April, more than held their own for long periods.
The best chances were split in the opening half, Willian and Santiago Vergini each hitting the woodwork.
Sunderland had the better opportunities after the break and Chelsea - who seemed fortunate not to be reduced to 10 men when Diego Costa was only booked for an apparent elbow on Wes Brown - will have been relieved to leave with their unbeaten record intact.
The early signs were ominous for the home side as Chelsea knocked the ball around with the confidence of a side topping the standings.
Yet Sunderland, driven by a raucous crowd and the tough-tackling Lee Cattermole, began to find a foothold in the game, epitomised by Connor Wickham curling an effort just over the crossbar.
That was a rare journey forward for the inhibited hosts in the opening exchanges, with Chelsea almost breaking the deadlock when Willian's low drive struck the outside of the post.
Mourinho's side looked threatening every time they went forward and Sunderland were indebted to a fine sliding challenge from John O'Shea that denied Costa a seemingly certain goal.
The resolute defending of Gus Poyet's side was best summed up by Cattermole, who threw his body in the way of several goal-bound efforts.
Costel Pantilimon was also alert when his time came, brilliantly saving with his right leg to deny Branislav Ivanovic after the right-back had been freed by Willian's pass.
Sunderland fashioned a great opening of their own soon after, though, as Cattermole's deflected cross ran into the path of Vergini - who saw a volley scrape the crossbar.
The visitors came out with plenty of intent after the break, Pantilimon keeping out a Gary Cahill header from Cesc Fabregas' corner.
Willian was the next to threaten, striking narrowly wide from 20 yards as Chelsea began to turn the screw.
They could easily have been down to 10 men not long after, only for Kevin Friend to show Costa just a yellow card following his challenge on Brown.
Undeterred, Sunderland continued to grow in confidence and made life uncomfortable for their opponents.
And they almost went ahead with 11 minutes remaining, lively substitute Jozy Altidore wriggling his way into the area and seeing a close-range effort blocked.
Adam Johnson spurned an even better opportunity soon after, poking narrowly wide from 12 yards after Altidore had again caused problems.
Chelsea continued to look vulnerable, Johnson threatening again with a curling 20-yard effort that flew just wide, but there was to be no breakthrough for either side.comments