For the first time in Mourinho's managerial career, he has lost back-to-back home league games.
Lamela, Lo Celso and Reguilon were pictured at the gathering over the Christmas period, a photo of which was circulated on social media.
Premier League: Tottenham Hotspur, West Ham, Fulham players breach protocols by attending party; Burnley-Fulham postponed
Tottenham trio Erik Lamela, Sergio Reguilon and Giovani Lo Celso were pictured close together with West Ham’s Manuel Lanzini and other people inside a home.
FA Cup: Giovani Lo Celso, Erik Lamela score as Tottenham beat Middlesbrough in replay; Newcastle ease past Rochdale
A 1-1 draw at Middlesbrough brought the teams back to London for a replay, which Tottenham started well and took a two-goal lead after 15 minutes through Giovani Lo Celso and Erik Lamela
Premier League: Tottenham Hotspur do not have time to 'sit and cry' about injuries, says manager Mauricio Pochettino
Tottenham lost goalkeeper Hugo Lloris to a long term elbow injury, with the skipper undergoing surgery earlier this week, while midfielder Erik Lamela and defender Jan Vertonghen are sidelined with hamstring injuries
Champions League: Tottenham boss Mauricio Pochettino raises doubts about team's attitude after draw against Olympiakos
Tottenham manager Mauricio Pochettino questioned his side's attitude after letting a two-goal lead slip to draw 2-2 away to Olympiakos in their Champions League opener on Wednesday.
Fantasy Premier League, Gameweek 5 tips: Raheem Sterling's hot streak makes him top pick for captain; Wild Cards can wait
Get all the tips, predictions and updates you need ahead of Gameweek 5 of the Fantasy Premier League in our weekly FPL round up.
Premier League: Pep Guardiola's VAR woes continue as Manchester City suffer early setback in title defence
From Moura's goal, until the rather dramatic ending of the match, the game played out in predictable patterns, with spells of Manchester City possession ending in near-escapes and close shaves for Tottenham
Premier League: Manchester City held to draw by Tottenham following controversial VAR decision; Arsenal, Liverpool scrape through
City thought they had stolen three points when Gabriel Jesus fired home in stoppage-time, but their celebrations were curtailed when a VAR review showed Aymeric Laporte had flicked the ball on with his arm
Premier League: Tottenham Hotspur's battling Champions League run should spur title challenge, says Mauricio Pochettino
Tottenham boss Mauricio Pochettino believes his team should seek inspiration from an unlikely run to the last 16 of the Champions League to pose a Premier League title challenge.
Champions League: 'Average' Lionel Messi still fantastic, says Tottenham Hotspur manager Mauricio Pochettino
Messi scored twice in a virtuoso display as Barcelona bounced back from a three-game winless run in La Liga to move alongside Inter Milan at the top of Group B.
Harry Kane moved alongside Jermain Defoe as the joint fifth highest Tottenham scorer of all time on 143 as the London club emerged from a slump by beating Brighton 2-1 in the English Premier League on Saturday.
Champions League: Tottenham's Erik Lamela says teammates need to chip in with goals to take pressure off Harry Kane
Tottenham's Erik Lamela has stated that the club's attacking players need to take the pressure off of Harry Kane to provide the answers for the team, and that they need to chip in with more goals.
Premier League: Erik Lamela becomes third Tottenham Hotspur player to sign contract extension during pre-season
Argentine Erik Lamela has signed a new contract with Tottenham Hotspur, keeping him at White Hart Lane till 2022. Lamela has been sidelined by a spate of injuries in the last few years,
Tottenham Hotspur can quickly put their disappointing defeat at West Bromwich Albion behind them by ensuring Champions League qualification with victories in their two remaining matches, midfielder Erik Lamela has said.
Premier League: Mauricio Pochettino defends team selection after Tottenham Hotspur's draw against Brighton
Mauricio Pochettino made six changes to his starting line-up and then saw his team drop two points in their quest to secure Champions League qualification.
Premier League: Against inconsistent Chelsea, Tottenham Hotspur have ideal chance to end Stamford Bridge drought
Beating Chelsea in their own backyard could be the first step for Tottenham towards changing the course of history, for they might not find themselves thrust into such an opportune moment for years to come.
Tottenham Hotspur's Mauricio Pochettino says winning Premier League more important than FA Cup title
Tottenham are fourth in the Premier League, four points adrift of second-placed United, and travel to fifth-placed Chelsea, who are five points behind them.
Christian Eriksen proved Tottenham can thrive without Harry Kane as the Dane's double sent them into the FA Cup semi-finals with a 3-0 win at Swansea on Saturday.
Premier League: Tottenham Hotspur's Son Heung-Min stars but Harry Kane limps off in Bournemouth win; Arsenal beat Watford
Son Heung-Min ensured Tottenham Hotspur didn't pay a heavy price for an ankle injury suffered by Harry Kane as he scored twice in a win 4-1 at Bournemouth on Sunday.