The warning was not altogether serious and probably will not prompt feelings of fear at the Etihad Stadium. Nevertheless, after Johann Berg Gudmundsson had completed the transformation of a forgettable stalemate into a surprisingly emphatic win, the Burnley fans chorused: “Manchester City, we’re coming for you.” In all probability, they are not, but this was a reminder of the attributes that powered Burnley to seventh place two seasons ago. They possess a fearlessness and a capacity to get the better of more fancied teams. Ashley Barnes epitomises both traits and it felt entirely in character that he should upstage striking signings at either club. Barnes retains a combative streak and, if he felt his position was imperilled by Jay Rodriguez’s return to Turf Moor, this was an eloquent response. The Burnley-born striker was afforded a huge ovation, but confined to a six-minute cameo after Barnes had scored twice in swift succession. Southampton’s new £15 million (Dh66.2m) forward Che Adams almost found the net but Barnes, Burnley’s £450,000 bargain, did twice. “He hasn’t scored in pre-season but he didn’t look like a striker who hadn’t scored,” manager Sean Dyche said. Pound for pound, Barnes represents one of the best bits of business in the past decade. If there is a sense he goes under the radar, Dyche added: “I don’t think it bothers him.” The striker took his tally to 34 Premier League goals with two crisp strikes. Burnley had failed to register a shot on target in the first hour but Southampton afforded them an opening with a mistake that led to a capitulation that angered manager Ralph Hasenhuttl. “It is the Premier League, it goes quick when you make mistakes,” the Austrian said. “We lost it for 12 minutes and it is not acceptable.” The catalyst for a collapse came when Jannik Vestergaard misjudged Erik Pieters’ hopeful punt forward. Barnes latched on to it and drilled a half-volley past Angus Gunn. “A fantastic touch and finish, it was great skill,” Dyche said. Barnes was similarly clinical when Pieters marked his Burnley bow with an altogether more convincing assist. He delivered the cross that the elusive Barnes met on the half-volley. The impression that Burnley were sharper than Southampton was reinforced when Gudmundsson robbed Ryan Bertrand to race away and add the third from an awkward angle. “Great finish,” said Dyche, though Gudmundsson’s challenge meant Burnley endured a wait while technology was consulted before the goal was ratified. VAR had denied Burnley a goal earlier, with Barnes rightly ruled offside before he set up Chris Wood for a tap in. It had enabled Adams to escape an early departure. His challenge on Ben Mee was reviewed, and the striker spared a red card. It would have been an ignominious way to mark his rise from Ilkeston Town to the top flight. The arrival from Birmingham almost made an immediate impact, volleying Yan Valery’s cross just wide. Forceful and a focal point, Adams offered encouragement, despite the result. There were signs of an embryonic understanding with Nathan Redmond and the former Claret Danny Ings. Redmond would have struck but for a stunning save from Nick Pope, making his first league appearance since being a part of the 2018 World Cup squad and justifying his selection by tipping Redmond’s menacing shot over the bar. Tom Heaton’s sale afforded Pope an opportunity, with Sean Dyche justified in benching Joe Hart. While each side started with a solitary debutant, the summer trading could yet reshape another pecking order. Southampton signed centre-back Kevin Danso on Thursday. “It is important to have more alternatives in the defence, not only this game showed it,” Hasenhuttl added. He showed Vestergaard little sympathy. “I don’t know why the centre-back missed this ball.” But with it, Southampton lost their chance to make a solid start.