While the defeat was Chelsea's ninth, prolonging their position a mere point above the relegation places, Leicester have lost only once and lead Arsenal, City and Manchester United.
This is no small sample size aberration, either. The Premier League is almost halfway through the season. So, while for now it will be whispered instead of shouted, the question must be asked ...
What would be the biggest shock? Unfancied Leicester City claiming the title or champions Chelsea being relegated to the second tier?
Let's start at the top. What Leicester are accomplishing is scarcely believable, but not without precedent.
Far more phenomenal was Brian Clough's accomplishments with Nottingham Forest in the late 1970s, taking the second division club to the top-flight title and two European Cups. And after the boom of the Premier League but before the birth of the traditional Big Four, Blackburn Rovers rode an influx of cash to the 1995 championship, becoming the only club other than United (13 titles), Chelsea (four), Arsenal (three) and City (two) to claim that honour.
Leicester have received assistance from no wealthy benefactor; there was nothing resembling a squad overhaul in the off-season. But Claudio Ranieri has his unfancied squad playing a fluent brand of football, sparked by the unforseen brilliance of Jamie Vardy and Riyad Mahrez.
Since their season began with a 4-2 thumping of Sunderland, the Foxes have outplayed and out-thought their opponents, suffering a solitary setback against Arsenal while leading the league with 34 goals.
None of this was anticipated. Leicester started the season paying $1000 at the TAB to emerge triumphant come May.
There's still some way before any optimistic punters can cash those bets, though, and the proof of Leicester's title contention will lie in the Christmas pudding.
Their next three games are away to Everton, away to Liverpool and home to Manchester City. Come through that stretch relatively unscathed and the impossible may become slightly more believable.
Speaking of impossible, how about Roman Abramovich's glamour club slumming it in the Championship, spending their Saturdays travelling to exotic locales like Huddersfield and Brentford? How about Jose Mourinho, a managerial master who has won championships in four countries, being fired before the New Year?
Mourinho was at his egotistical best when he uttered the words listed on the right of this page but, in truth, he did have a right to feel betrayed. Chelsea's players clearly quit on their coach, because there's no other explanation for magicians such as Eden Hazard apparently forgetting every one of their tricks.
What Chelsea are enduring is astonishing but, like Leicester's fairytale, this has happened before. Manchester City in the late 1930s were sent down to the second division the season after claiming the silverware, and the first-to-worst slide in a top European league has also happened in Germany (Nurnberg in 1968-69).
So which result - Leicester winning the league or Chelsea being relegated - rates higher on the surprise scale? Only one side can be champions while three spaces are open for demotion, but I'm still awarding a slight edge to Chelsea.
The top of the Premier League is at one of its lowest ebbs, with both Manchester clubs lacking inspiration and Arsenal following the brilliant with the bizarre.
The title appears up for grabs and Leicester have earned their current position through flair rather than fortune.
They could keep winning. Chelsea's talent-laden team, however, surely can't keep losing. Surely ...
