Chelsea wasted a chance to cement their place in the Premier League's top four as a superb display from Southampton goalkeeper Angus Gunn gave his struggling side a 0-0 draw on Wednesday.
Maurizio Sarri's team remain in fourth place, but they are now just three points ahead of fifth placed Arsenal in the race to qualify for next season's Champions League.
It was a frustrating evening for Chelsea, who dominated possession but lacked any cutting edge, maintaining a worrying sequence for Sarri.
His side failed to score for the third time in their last five Premier League games at Stamford Bridge, raising more questions about Chelsea's need for a top-class striker in the January transfer window.
With Olivier Giroud sidelined after suffering an ankle injury in Sunday's win at Crystal Palace, Sarri opted to recall misfiring striker Alvaro Morata.
Morata has played so badly this season that Sarri had used Belgian winger Eden Hazard in the central forward's role recently rather than turn to the Spaniard, who had managed only seven goals this term and none in the league since November 4.
But, once again, former Real Madrid star Morata looked completely bereft of touch and confidence.
It was no surprise Morata wasted a golden opportunity to open the scoring when he met Cesar Azpilicueta's long pass with a tame header straight at 22-year-old Gunn -- the son of ex-Norwich stopper Bryan Gunn.
Southampton avoided a third consecutive defeat with a well-drilled performance, but they still dropped into the relegation zone.
Having announced the signing of Borussia Dortmund midfielder Christian Pulisic earlier in the day, Chelsea are planning ahead following a season of inconsistent displays from Willian and Pedro on the right flank.
United States international Pulisic will return to Dortmund on loan before completing his move to Chelsea in the close-season.
For the moment, Sarri continues to use Willian, but the Brazilian's bid to prove his worth was ruined when he was forced off with an injury late in the first half.