Southampton secured their first clean sheet in 11 Premier League games as Ralph Hasenhuttl’s side produced a battling performance to frustrate Chelsea and secure a point at Stamford Bridge.The Blues, fourth in the Premier League, had more than 70% possession but could not break down a well-organised and disciplined Saints side.Chelsea’s best chance fell to Eden Hazard, but his well-hit shot was saved by Premier League debutant Angus Gunn.Alvaro Morata thought he had scored when he put the ball into the net midway through the second half, but it was ruled out as he was given offsideSouthampton offered little as an attacking force, with one Oriol Romeu shot easily saved by Kepa Arrizabalaga.The hosts wanted a late penalty as Marcos Alonso went to ground under a challenge from Shane Long, but referee Jonathan Moss was not interested in Chelsea’s appeals.Despite the hard-earned point, Southampton still drop into the bottom three as they fall below Burnley into 18th after the Clarets’ 2-1 win at Huddersfield.Before the game, Chelsea head coach Maurizio Sarri said the club “was in trouble” because of their injury problems and the fact they would have to play “every three days” in January.Those problems worsened in the first half as Willian, following a strong challenge from Maya Yoshida, limped off to be replaced by Ruben Loftus-Cheek, himself only just returning to contention after a back injury.It means the Brazilian joins Olivier Giroud (ankle), Pedro (hamstring) and Callum Hudson-Odoi (hamstring) as attacking options that are unavailable for the Blues, who could play as many as eight games this month.Earlier on Wednesday, Chelsea announced they have signed 20-year-old Borussia Dortmund forward Christian Pulisic for 64m euros (£58m), although he will also not feature for the Blues in 2018-19 as he will be loaned back to the German club until the end of the season.This performance shows why Sarri has opted to strengthen his squad as once again Morata failed to impress up front with the Spaniard failing to score for the seventh consecutive Premier League game.He had a weak header easily saved after Cesar Azpilicueta’s long ball forward and looked to have ended his goalless run but was denied by the assistant referee’s flag as he was judged offside.The draw means Chelsea are now 10 points behind leaders Liverpool, who play their game in hand, away at Manchester City, on Thursday.Southampton manager Hasenhuttl opted to make eight changes to the side that began the 3-1 loss against Manchester City on Sunday, including a Premier League debut for 22-year-old goalkeeper Gunn, son of ex-Norwich goalkeeper Bryan.Gunn did well to quickly come off his line and clear the danger on a couple of times in the first half and also denied Hazard, with the Belgian’s powerful shot hitting him in the face.Hasenhuttl had organised his team well and they proved hard to break down with a back five and at times five midfielders in front of them with Danny Ings and then his replacement Shane Long, sometimes operating as their lone striker, but often dropping back to help their team-mates further.The tactics worked as the hosts, despite having 72% of possession, could only manage two shots on target in the first half – Hazard’s effort saved by Gunn and Morata’s weak header.Gunn, who cost the Saints £10m in a summer move from Manchester City, was busier in the second half as he parried a Hazard effort, caught a rising Jorginho shot, held on to a Morata strike and denied Alonso in stoppage time.The final whistle saw Hasenhuttl punch the air in celebration as his side picked up their seventh point in his six games in charge – including matches against three of the top five – Arsenal, Manchester City and now Chelsea.It was also only the fifth time Southampton had stopped the opposition from scoring in 21 Premier League matches in 2018-19 and was their first clean sheet since 27 October when they drew 0-0 at home with Newcastle.Southampton manager Ralph Hasenhuttl told BBC Sport: “I think it was very hard work against the ball. The guys were brave, sometimes pressing high, sometimes deeper. We didn’t give so many chances away, they have fantastic quality and to defend every attack is not easy, but with our mentality we deserved a point.“In the last 30 minutes you feel tired, we had to close the gaps and if you have guy like Eden Hazard dribbling at you, you need a lot of players near him to stop him.“We made the right decision to change so many players against Manchester City to keep them fresh for today. I don’t want to say we gave the Manchester City game away but we had more chances today. It was an amazing fight we gave.”On goalkeeper Gunn, who kept a clean sheet on his debut, Hasenhuttl added: “The guy showed he is a very forward defensive goalkeeper. We knew about Chelsea’s chipped balls forward and we told him to be brave. He made some good saves and I’m happy with him.”Chelsea entertain Championship side Nottingham Forest in the third round of the FA Cup on Saturday, 5 January (15:00 GMT) and then face Tottenham away from home in the first leg of the Carabao Cup semi-final on Tuesday, 8 January, before returning to league action on Saturday, 12 January when they play Newcastle.Southampton play in the FA Cup at Derby on Saturday (15:00 GMT), before another trip to the East Midlands to face Leicester in the Premier League a week later.