Jose Mourinho felt Manchester United were denied a clear penalty in their 2-1 defeat to Manchester City and claimed the decision was the "crucial mistake" in Sunday's derby.
The Premier League leaders secured a 14th win in a row – a record for a single season in the English top flight – and an 11-point lead at the Premier League summit thanks to goals from David Silva and Nicolas Otamendi either side of a Marcus Rashford strike.
City dominated possession at Old Trafford and looked unlikely to allow United back into the game for a second time after Otamendi's winner, although there was a controversial incident with 11 minutes left when Ander Herrera was booked for diving after being clipped by the Argentine defender in the penalty area.
Mourinho believes that decision from referee Michael Oliver cost his side the match and pointed to a similar incident last season, when Claudio Bravo escaped punishment for a lunge on Wayne Rooney as City saw out a 2-1 victory.
The United boss told Sky Sports: "Clear penalty. I'm sorry for us, for Michael, I think he had a good game but it's a clear penalty. Don't you agree?
"The referee made a mistake, which can happen. Last season, we had a similar situation against Manchester City, who were winning 2-1 and Mr [Mark] Clattenburg didn't see the penalty of Bravo on Rooney.
"I'm sorry for Michael Oliver because he had a good performance.
"He is a human being, he tried his best, he was very committed to have a good match, which I think he had. But he made one mistake and it was the crucial mistake for the result of the match."
9 – Jose Mourinho has lost more matches in all competitions against Pep Guardiola than versus any other manager. Foe. pic.twitter.com/jMleQQnIL6— OptaJoe (@OptaJoe) December 10, 2017
United had eight shots to City's 14 and managed just 35 per cent of the possession, but Mourinho was left angry at the way his side conceded twice after failing to clear their lines from set-pieces.
He did, however, credit the visitors for their approach as they ended United's 40-match unbeaten run at home, which stretched all the way back to the derby defeat last September.
Mourinho said: "They scored two very bad goals. They scored two goals that are quite unbelievable to concede and when you concede two goals like this, in a match of this dimension, you obviously feel bad because now you're all going to speak about what they do well, what they're good at, and in the end what they're good at, they were not good at, and they scored two goals out of nothing.
"We did good things, we did bad things. We have a complete dedication to the match, every player trying to do their best. We know they're very good in ball possession, very good at bringing their full-backs inside and they also had an extra man with the striker dropping back.
"Even if you try to press, it's really difficult to recover the ball, so credit to them for that quality they have in their principles of play."
|Orioles become first pro team to wear braille jerseys|
|Klopp hails ´brilliant´ Henderson|
|PSG attack lacked aggression, says Tuchel|
|Atletico Tucuman 0 Gremio 2: Libertadores holders draw first blood in QFs|
|Thomas plays down wrist worry|
|Rakitic wants more from Barcelona hat-trick hero Messi|
|My players aren´t s*** – Pochettino defends Spurs squad|
|Cubs reliever Morrow won´t return this season|
|Tebow expected to be back in Mets organisation next season|
|Inter can compete against anyone – Icardi revels in Champions League victory|
|Tuchel: PSG loss to Liverpool not logical or correct|
|Sturridge in best shape I´ve seen – Klopp|
|Milojevic celebrates ´fantastic´ occasion after Red Star´s 26-year wait|
|Rodrigo and Simeone salute Griezmann display|
|Seahawks DE Clark on Bears QB Trubisky: He´s nothing special|
|Carroll says Wilson has been ´over-trying a little bit´|
|Judge returns to Yankees´ starting lineup|
|Napoli boss Ancelotti takes aim at Red Star time wasting|
|Favre admits young Dortmund stars struggled in Bruges|
|Otavio would trade goal for Porto victory as he bemoans Schalke draw|
|Championship Review: Pacesetters Leeds crush Preston, Villa end five-game winless run|
|Neymar world-class but not a defender - Klopp says Liverpool targeted PSG star|
|Waiters injury update: Heat guard unlikely to be ready for start of season|
|Gojowczyk eliminates returning Tsonga in Metz|
|Liverpool enjoying best start in 57 years after PSG win|
|Galatasaray 3 Lokomotiv Moscow 0: Terim´s side make light work of Russians|
|Club Brugge 0 Borussia Dortmund 1: Super sub Pulisic scores late winner|
|Schalke 1 Porto 1: Fahrmann saves one penalty, but Otavio scores another|
|Red Star Belgrade 0 Napoli 0: Points shared as Italians fail to make possession pay|
|Liverpool 3 Paris Saint-Germain 2: Firmino strikes late as Reds edge five-goal thriller|
|Monaco 1 Atletico Madrid 2: Costa and Gimenez seal comfortable win|
|Chaos reigns in Serie B as league denies suspension claim|
|India secure Asia Cup victory despite valiant Hong Kong effort|
|Messi makes "extraordinary routine", says Valverde after Barca star surpasses Ronaldo|
|Spalletti´s Inter to take heart from Tottenham turnaround|
|Casillas features in landmark 20th Champions League campaign|
|Spurs deserved more from best performance of the season - Pochettino|
|Brown absent from Steelers facility on Monday due to ´personal matter´|
|Toronto´s Bussey given eight-match biting ban|
|Barcelona 4 PSV 0: Marvellous Messi lights up Camp Nou|
|Inter 2 Tottenham 1: Icardi, Vecino complete dramatic late turnaround|
|Allegri, Chiellini defend Costa over spitting ban|
|Firmino only fit enough for bench duty|
|Kovac applauds Sanches ahead of Benfica homecoming|
|Tomlin confirms Steelers WR Brown was absent from facility on Monday|
|Mourinho tells United to follow Federer´s lead amid Young Boys pitch concerns|
|Costa banned for four Serie A matches for spitting|
|PGA Tour announces changes to FedEx Cup Playoffs format|
|Rashford to start against Young Boys, Mourinho confirms|
|Ryder Cup heading to Congressional in 2036|
|I never listen to stupid things - De Gea unconcerned by criticism|
|Aguero trains as Mendy sits out Man City session|
|Lampard fined after accepting improper conduct charge|
|Serie B suspended after Pro Vercelli win appeal|
|Mitchell returns to England as defence coach|
|Brady completes Cornet upset in Guangzhou|
|Lopetegui giving no guarantees to ´fighter´ Navas|
|Di Francesco denies racially abusing Costa|
|Saunders apologises for ´sickening´ online video|
|Tianjin Quanjian 0 Kashima Antlers 3 (0-5 agg): Semi-final spot booked in resounding fashion|
|Madrid cannot live on Ronaldo´s glories, warns Ramos|
|Real Madrid are Champions League favourites, insists Man City coach Arteta|
|Stokes & Hales charged with bringing game into disrepute|
|Stephens slips to Vekic defeat in Tokyo|
|Simeone should teach Griezmann values - Ramos questions Ballon d´Or ambition|
|Arteta ready to step into Guardiola´s shoes after missing out on Arsenal job|
|Naive or scheming - Ozil´s agent slams Kroos, Neuer and Muller|
|Bolton´s Darby forced to retire after Motor Neurone Disease diagnosis|
|Root vows dressing support for Moeen over Ashes abuse claims|
|Madrid more dangerous without Ronaldo - Dani Alves|