On 17 December 2015, Chelsea sacked Jose Mourinho for a second time, seven months after he had led them to the Premier League title, with the club 16th and only one point above the relegation zone.
Fast forward a year and the Blues, who finished the 2015-16 season in 10th after Guus Hiddink steadied things, are nine points clear as they chase a fifth Premier League title.
All four of their previous titles – in 2004-05, 2005-06, 2009-10 and 2014-15 – have come having topped the table at Christmas.
Only several fine saves from Palace goalkeeper Wayne Hennessey denied Chelsea a wider margin of victory at Selhurst Park, the Welshman doing well to deny N’Golo Kante and Alonso, who later struck the woodwork.
Chelsea have the top goalscorer in the league in Costa and are also continuing to impress at the other end of the pitch through goalkeeper Thibaut Courtois, centre-halves Azpilicueta, Gary Cahill and David Luiz, and the cover provided in front of them by Nemanja Matic and Kante.
Hosts Palace did not have a shot on target in the first half and Chelsea defended superbly to deny them any clear-cut opportunities in the second half.
Conte’s side have now conceded only two goals in 11 Premier League matches since changing to three at the back following a 3-0 defeat by Arsenal on 24 September.
If they can continue this defensive excellence throughout the rest of the season, the title will surely be heading back to Stamford Bridge.
Palace’s defensive struggles continue
While it has been a fine 12 months for Chelsea, the same cannot be said for Palace.
Yes, they reached the FA Cup final, losing 2-1 after extra time to Manchester United, but they have won only six of 36 Premier League games in 2016.
They have kept just one clean sheet in 22 top-flight matches, and are only one point above the relegation zone.
Scott Dann was at fault for Costa’s goal – he was caught not watching the ball and failed to get off the ground to challenge.
Man of the match – Cesar Azpilicueta (Chelsea)
Palace’s poor record in derbies continues
Palace have now won only one home league game against Chelsea since 1990.
Chelsea defender Gary Cahill was making his 300th Premier League appearance.
Chelsea have become the third team to win 500 Premier League games, after Arsenal (512) and Manchester United (593).
Six of the past seven teams to top the Premier League at Christmas have gone on to lift the trophy that season.
Palace are winless in nine Premier League London derbies since a 2-1 victory at Chelsea in August 2015 (drew two, lost seven).
Antonio Conte is the first Premier League manager to win 14 of his opening 17 games in the competition.
Diego Costa has scored 50 goals in all competitions for Chelsea; 17 more than any other player for the club since his debut
What they said
Crystal Palace manager Alan Pardew: “It was a strong performance but they did not give us anything and that was as good a defensive display that we have seen. Once we conceded, it was very difficult.
“We could not get Wilfried Zaha isolated. We kept the ball and passed it well, but the final pass was very difficult. For our offensive players, it was the toughest game they have had. This team is not getting what it is deserves. That will change.
“We have all come up against this system before but it is with outstanding players. They ask questions and do not make errors. N’Golo Kante gives so much energy like he had at Leicester and fills holes which goes unnoticed.
“You don’t really expect a centre-half [Azpilicueta] to have that quality – it was a Cesc Fabregas-type ball for the goal and it was a crucial one before half time. I take heart from the last two performances. We deserved something.”
Chelsea boss Antonio Conte: “The run is fantastic. Congratulations to my players, not me. I am pleased for them because they deserve this. I see every single moment, every day. It is commitment, the way we prepare for the game and the way they fight. I am pleased for the fans who are fantastic home and away and who push us.
“We can improve though. You can always improve in different aspects. I am pleased with this level we have reached, but it is important to understand we are only at the 17th game in the season. We must not look at the table. We must not look at our rivals and continue working hard ourselves.
“We have reached a good balance between offence and defence. In some moments, our goalkeeper has been decisive. We dominated the last game but Thibaut made a fantastic save. After last season when he conceded lots of goals, this season is very good for him. We attack and defend as a team.”
Both sides are in Premier League action again on Boxing Day, with Crystal Palace at Watford in the early game (12:30 GMT) and Chelsea hosting Bournemouth (15:00 GMT).
Chelsea will be without 13-goal top goalscorer Costa as a first-half foul on Joe Ledley saw the Spain striker get booked, his fifth yellow card of the season, and he will now serve a one-match suspension. Team-mate Kante will also be missing as he was also shown a fifth yellow card, following a number of fouls.