By Aimee Lewis, BBC Sport
Chelsea secured their first victory in Guus Hiddink's second spell as boss to move six points clear of relegation with a deserved win at Crystal Palace.
Oscar put the Blues ahead against the run of play, tapping home after being put through by Diego Costa. Once they scored Chelsea dominated, deservedly doubling their advantage with a spectacular Willian strike.
Costa sealed the win with a tap-in for a goal his performance deserved after Palace failed to clear Willian's shot.
Interim boss Hiddink, who guided Chelsea to third in the Premier League, a Champions League semi-final and the FA Cup in his first spell at the club, remains unbeaten since taking over from Jose Mourinho last month.
The Blues' four-match run without defeat is their longest this season and moves last year's champions to 14th in the league, still 13 points adrift of a Champions League spot.
Chelsea's away form in the first half of the season has been dire, with just six points collected on their travels. Only bottom two clubs Aston Villa and Sunderland have fared worse. In beating seventh-placed Palace for their first away win since August, the Blues made a convincing case that the second half of the season might be more fruitful.>
Hiddink said he needed leaders to pull the club out of relegation trouble and in Costa the Dutchman had a player in that mould, driving his team forward at Selhurst Park and playing a part in all three goals.
Like the rest of the Blues squad during this season's dreadful title defence, the Spaniard - who had missed the goalless draw at Manchester United because of suspension - has been below par, but he gave one of his best displays of the campaign.
John Mikel Obi also shone, providing much-needed ballast to the Chelsea midfield.
The one disappointment for Hiddink was the injury to Eden Hazard, which ended the Belgian's match after just 15 minutes.
Before the match Hiddink had said last year's player of the season was "back in shape" after suffering a hip injury against Leicester and sustaining a knock in Monday's draw at Manchester United.
Ultimately, Chelsea did not need Hazard against Palace with the impressive forward trio of Costa, Willian and Oscar creating plenty in his absence.
It was Palace's first defeat in seven matches and they clearly missed key players, although Eagles boss Alan Pardew admitted that even with the likes of suspended Yohan Cabaye in the team his men would have struggled against Chelsea in such form.
Palace must 'wipe our nose and move on'
The hosts, though, are a far less formidable side without the creativity of top scorer Cabaye in midfield, the pace of Yannick Bolasie on the flanks and Connor Wickham up front.
Palace are now without a win or a goal in their past three games, with Bolasie and Wickham not having played since the goalless Boxing Day draw against Bournemouth.
However, Pardew's side had their chances with Wilfried Zaha - making his 200th appearance for the club - shooting wide with the score goalless and scuffing another opportunity just before Willian scored.
The Spaniard played a key part in securing Chelsea their biggest league win of the season, assisting Oscar and claiming his seventh goal this term. He covered more than 10k in a tenacious display.
Chelsea interim boss Guus Hiddink: "Do not go over the top, it is the first win after a worrying period with two draws so the team desperately needed the win and it was convincing.
"Everyone knows we have a lot of quality in our team, but sometimes champions have a tendency to be complacent and it can be difficult to get back and then wonder why we were champions.
"There is a long way to go, mathematically the possibility of Champions League is still there. The league is so strong but as long as we play like we did today I will be happy."
Crystal Palace manager Alan Pardew: "We were not at our strongest, we were missing key players and could not play our natural game.
"We will be looking at the market in case something comes through. It is important we kick into gear in the second half of the season. Things did not go our way and we have to respond and I have every confidence in this group that we will be in and around the top 10."
This is Chelsea's first away victory in their last eight Premier League away matches (losing four and drawing three) and the first since August when they beat West Brom 3-2 at the Hawthorns.
Crystal Palace have enjoyed just two wins in their last seven home league games (drawing two and losing three). Oscar has netted two in his last four in all competitions for Chelsea after scoring just one in the 14 before that.
Diego Costa's assist was his first in his last 20 appearances in all competitions for Chelsea. Seven of Willian's eight goals for Chelsea this season in all competitions have come from outside the box.
Costa has had a hand in four goals in his last two league games (three goals, one assist), the same total he managed in his previous 14 league appearances this season.
Chelsea registered their biggest league win in almost a year, since beating Swansea 5-0 on January 17th 2015.