Chelsea ended the year with just one win in five as Anwar El Ghazi's equaliser earned Aston Villa a 1-1 draw at Stamford Bridge.
Olivier Giroud, so often the scourge of the visitors, put Chelsea ahead with a fine near-post header from Ben Chilwell's cross (34), meaning the striker has now scored in 10 goals in 10 games against Villa, and has eight in eight for Chelsea.
But El Ghazi's far-post finish through the legs of Edouard Mendy from Matty Cash's cross (50) angered Chelsea, with the hosts wanting a foul on Andreas Christensen from Jack Grealish in the build-up and a handball from Matt Targett.
Both sides did their best to win it; John McGinn struck the bar with a brilliant long-range effort, sub Jacob Ramsey curled inches wide, while for Chelsea Christian Pulisic was denied by Emi Martinez's save and Chilwell lashed a beautiful volley just wide in stoppage time.
The result means Villa move up to fifth, six points off leaders Liverpool with a game in hand, while Chelsea go sixth on the same points, but having played two games more than Villa.
Chelsea: Mendy (5), Azpilicueta (5), Christensen (5), Rudiger (6), Chilwell (7), Jorginho (6), Kante (6), Mount (6), Hudson-Odoi (6), Pulisic (7), Giroud (7)
Subs: Werner (5), Havertz (5)
Aston Villa: Martinez (7), Cash (7), Konsa (7), Hause (7), Targett (7), Luiz (7), McGinn (8), Grealish (6), Traore (5), El Ghazi (7), Watkins (6)
Subs: Ramsey (NA), Davis (NA)
Man of the match: John McGinn
How Villa fought back to earn useful point
After the 3-1 defeat by Arsenal on Boxing Day, Frank Lampard picked a Chelsea XI that included just two of their six summer signings, and the hosts went back to basics with a dogged first-half performance following three defeats in four.
Grealish was, on the whole, kept quiet in the first half, but managed to test Mendy from the edge of the box after being shown onto his right foot. Grealish himself then sloppily gave the ball away at the other end, only for Pulisic to strike wide after pouncing when he should have hit the target.
Kourtney Hause then headed over unmarked from a Grealish free-kick, while Cash blazed over after Mendy had fumbled a cross.
But it was Giroud - who else? - who netted the opener. After Chilwell was found in space on the left, his delivery was waist-height for Giroud, but the Frenchman stooped down low brilliantly to flick a header near post past the reach of Martinez.
It ended Villa's run of over seven hours without conceding, while Giroud has now also scored in seven straight games against Villa.
Chelsea could smell a second as Villa retreated after the goal - Villa struggled on Chelsea's right as Chilwell routinely found time to cross - but Villa levelled as El Ghazi got his fifth goal in five games having scored just four in his previous 37.
Advantage had initially been played to Villa as Christensen collided with Grealish, but the Villa man recovered before spreading out wide to Cash, who found El Ghazi unmarked at the near post to turn home from a few yards out with Christensen still down.
Replays showed Christensen was hurt by Grealish's dangling leg as he looked for the foul, but the defender had also caught Grealish with his back foot. VAR couldn't review, as the initial ball into the box had been cleared and therefore the phase of play had been reset. Frank Lampard also claimed after the game he thought Matt Targett had handled in the build-up.
The game was poised as both sides pushed for a winner; McGinn, tireless and determined throughout, struck the bar with a wonderful 30-yard effort, while Martinez tipped over Pulisic's own long-range effort.
Villa sub Ramsey's first action was to curl inches wide of the far post from the edge of the box. Chelsea's own sub Werner lifted an effort over the bar as his search for a goal reached nearly 700 minutes.
Frank Lampard brought in six new faces in a major shake-up following their defeat at Arsenal. Three were at the back - Azpilicueta, Christensen and Rudiger came in for James, Silva and Zouma; Zouma and James didn't even make the bench.
Elsewhere, Abraham and Werner dropped to the bench alongside midfielder Kovacic, with Giroud, Hudson-Odoi and Jorginho coming in.
Villa made just the one change from the 3-0 win over Palace on Boxing Day as Konsa replaced the suspended Mings. Barkley was ineligible against his parent club.
Villa's hearts were in mouths in stoppage time as Chilwell lashed a first-time volley from an angle just wide, but the draw was fair as Dean Smith's side showed again how competitive they are, having lost just one of their last nine away games.
Chelsea, however, end 2020 on a negative note having entered the winter period with much promise, taking just four points from a possible 15 since December 12.
What the managers said
Chelsea boss Frank Lampard: "I was pleased, I'm not disappointed with anything tonight other than the fact we conceded that goal, and didn't score another.
"I think there was a handball, and the fourth official was very close to us, I'm not sure (why) it wasn't given, it should have been handball.
"I haven't seen the Christensen-Grealish incident. I didn't think there was much in it at the time, I'm not sure it was a foul or not. I haven't reviewed that referee-wise."
Aston Villa boss Dean Smith: "I'm pleased with the point, it's a really good point. This is a tough place to come, they've rotated what is a really strong squad.
"There were spells from both teams in the game, we started better, they came into it, we had to weather the storm after they scored. We found a really good balance again between defending and attacking. The energy levels of my players was incredible seeing as we only played 48 hours ago."
- Chelsea have lost just one of their last 14 Premier League home games (W10 D3), with that lone defeat coming against Liverpool earlier this season.
- Since losing at Liverpool in July, Aston Villa have only suffered one defeat in their last nine away games in the Premier League (W5 D3).
- Since his Premier League debut in August 2012, Olivier Giroud has scored more headed goals than any other player in the competition (32).
- Ben Chilwell equalled his Premier League season-best tally of four assists, with the Chelsea defender having as many goal involvements in this campaign as 2019/20 (6 - 2 goals, 4 assists).
Chelsea are scheduled to host Manchester City in the Premier League on Sunday January 3 at 16:30h. GMT, before then hosting Morecambe on Sunday January 10 in the FA Cup third round at 13.30h. GMT.
Villa now go to Manchester United on New Year's Day at 8pm, live on Sky Sports Premier League, before hosting Liverpool in the FA Cup third round on January 8 and 19.45h. CET.