Last-placed Watford delivered a shocking blow to a listless Manchester United side at Vicarage Road, as they secured a well-deserved 2-0 win over their northern rivals.United No.1 David De Gea made a mess of a routine save and gifted the home side the opening goal in the 50th minute after failing to save Ismaïla Sarr's weak shot following a set-piece situation. The goal was The Hornets' first under new manager Nigel Pearson.Watford have won a game at home in the Premier League for the first time since April 2019.LDLLLLDDDLLDWA huge win for the Hornets. 🐝 pic.twitter.com/lAJkPRYJYn— Squawka Football (@Squawka) December 22, 2019The second half got even better for the hosts as they were awarded a penalty just four minutes after they opened the scoring, as the tricky Sarr was brought down by right-back Aaron Wan-Bissaka. Captain Troy Deeney made no mistake as he commandingly smashed it home from the spot, sending De Gea the wrong way.The Red Devils' defensive woes were once brought to the fore, while they also lacked vision going forward. They have now failed to keep a clean sheet in the last 13 league outings.So, as Watford won their first home game and just their second game of the season, we round up the major talking points from the game.#3 David De Gea's season goes from bad to worse as he commits an absolute howlerWatford FC v Manchester United - Premier LeagueIt was just two seasons ago that Spaniard David De Gea had won his maiden Golden Glove in the Premier League, managing a shut-out in 18 of his 37 games during the 2017-18 campaign.Early in the second half, Watford were awarded a free-kick in United's half, though not in a dangerous position. Will Hughes delivered a ball into the box, which found its way to Sarr, who failed to connect convincingly with his volley. But De Gea was caught napping, as he allowed the ball to pass right through his gloves and into the net, virtually gifting the lead to the hosts in the 50th minute.He has seemed out of touch since the last season and that poor run of form has also caught up with him this season. He has already let in 22 goals this season and has the worst clean sheet record in the English top-flight, with just two to his name thus far. He only managed a single save throughout the game.6 - Since the start of last season, no player has made more errors leading to goals in the Premier League than David de Gea (6). Gifts. #WATMUN pic.twitter.com/RIpNYWZYi5— OptaJoe (@OptaJoe) December 22, 2019Though he is still a top goalie, with the ability to pull off some eye-catching saves on his day, he has been anything but world-class since extending his contract with the club last summer.Also See: Premier League, Premier League table