Investors kept faith with the group, sending the price up 4%, after chief executive Michael Sharp pledged to refine its promotional strategy and improve its multi-channel offering through much faster delivery times.
The rise came as the wider market fell amid further concerns over Ukraine, as it sent tanks and troops to reclaim government buildings occupied by pro-Russian gunmen in the east of the country. The FTSE 100 Index ended 42.2 points down at 6541.6. Sentiment was also affected by the latest data causing uncertainty on the health of the Chinese economy. Germany's Dax was down sharply while France's Cac 40 also fell.
In New York, the Dow Jones Industrial Average initially looked to build on previous session gains sparked by better-than-expected US retail sales figures before also being pulled into the red by the global gloom.
On currency markets, sterling was little affected by official figures showing inflation fell to 1.6% in March, the sixth monthly decline in succession - as widely expected. The pound held firm at 1.67 US dollars and 1.21 euros.
In equities, Debenhams, which reported a 24.5% fall in half-year profits to £85.2 million, lifted 3.4p to 81p in the FTSE 250 Index, though it was still a far cry from the 114p seen in October.
The profits plunge had already been pencilled in after the group issued a stark warning on earnings following a disappointing Christmas trading period, while analysts said sales in January and February were better than expected.
Matthew McEachran at N+1 Singer said the trading update showed "small strategic modifications" which were first steps towards weaning customers off the discounts that have hit its profit margins.
Brewer SABMiller was one of the biggest top-flight fallers after it said currency headwinds will impact full-year results. Volumes grew by 2% over the year but this was not enough to prevent shares from falling 2% or 71.5p to 3052.5p, with the drop reversing some of the gains seen in the stock in recent weeks.
G4S stock was also down, in the wake of a ratings downgrade for the outsourcing and security giant from Deutsche Bank. Shares fell 7.4p to 240.6p.
Meanwhile Imperial Tobacco was up as it announced it was to end cigarette manufacturing in the UK, under plans to close its Nottingham factory with the loss of up to 540 jobs. Shares rose 7p to 2481p.
The biggest FTSE 100 risers were Royal Mail, up 18p to 510p, United Utilities up 16p to 769.5p, SSE up 26p to 1495p and Severn Trent up 28p to 1787p.
The biggest fallers were Fresnillo, down 31p to 901.5p, Rio Tinto down 105.5p to 3302.5p, G4S down 7.4p to 240.6p and Aviva down 13.6p to 491.4p.