A 0.5% improvement in the eight weeks to Christmas Eve was not enough to save the beleaguered retailer from the deteriorating overall performance for general merchandise.
The group admitted that a series of discounts to drive seasonal sales - which included a pre-Christmas "Mega Day" with reductions of up to 30% on clothing lines - would hit profit margins when full-year results are reported later this year.
Chief executive Marc Bolland welcomed the improved Christmas performance with sales up in a "highly promotional market".
"However, an exceptionally unseasonal October, which saw GM sales down strongly, has resulted in a quarterly performance below our expectations," he added.
The sales slump was worse than expected and poorer than the previous quarter, when M&S posted a 1.3% decline.
Mr Bolland is likely to face renewed pressure over the performance, coming more than a year after he began a reshuffle of the brand's key fashion executives as the store tried to turn around its fortunes.
Food sales continued to grow, with record sales over the Christmas period and a biggest day ever of sales when £64 million of M&S groceries went through the check-outs on December 23.
But the like-for-like improvement of 1.6% over the quarter compared to 3.2% last time meant even this performance showed a slowdown.
Mr Bolland said growth in online sales of 23% was "strongly ahead of the market".