A change of formation has been the catalyst for Chelsea's recent improvement. Since switching from 4-2-3-1 to 3-4-3 after their 3-0 defeat by Arsenal at the Emirates Stadium, the Blues have won all four of their Premier League games without conceding a goal.
It's the system Conte has used throughout his coaching career, and it's taken no time for Chelsea's players to adapt. Defensively, the back three of Gary Cahill, David Luiz and Cesar Azpilicueta are afforded plenty of protection by Nemanja Matic and N'Golo Kante, and there's added support from wing-backs Marcos Alonso and Victor Moses.
"We've worked hard on the shape the manager's brought and we're getting the rewards," said Cahill after Sunday's victory. Opponents are struggling to create openings against Chelsea's packed defensive ranks. Southampton only mustered one shot on target at St Mary's, and the run of four consecutive clean sheets highlights Chelsea's new-found solidity.
"Conte's got them well-drilled," said Sky Sports pundit Graeme Souness. "They sit in and defend their box. They have a lot of players who are good at defending in the air and on the ground."
The new system has also unlocked Chelsea's attacking potential. The Blues are lethal on the break and clinical in front of goal. They beat Manchester United 4-0 despite having just 43.9 per cent of possession, and they recorded a similar figure against Southampton. Souness described their first-half display at St Mary's as a "masterclass in counter-attacking football". Southampton won't be the last team who struggle to contain them.
Hazard back to his best
Hazard has been the biggest beneficiary of the change of formation. The Belgian grew disillusioned on the left flank last season, but he has been given licence to roam in the new system and doesn't have to worry about defensive responsibilities. According to Opta, his average position has been even more advanced than Costa's in three of Chelsea's last four games.
Hazard is focusing on what he does best. His opener was brilliantly taken, and he has now scored more goals in 10 games (five) than he managed in 31 appearances last season. He was named man of the match for the second consecutive match after his starring role in last week's thrashing of Manchester United, and this was arguably an even better performance.
He combined brilliantly with Costa throughout, and his assist for the Spaniard's goal was one of five chances he created across the 90 minutes. Hazard was a constant threat. Southampton's defenders were reduced to fouling him more often than any other player, and Gary Neville was impressed by some of the positions he took up in central areas.
"It's impossible for a right-back to go there, it's impossible for a centre-back to come out, and it's a nightmare for a midfield player to think about him," Neville said. "He's just free and released. He's not stuck out on the left-hand side. He's there and he's always got five yards of space."
Hazard lost his way last season, but the 2014/15 Player of the Year is back to his old self under Conte, and Chelsea are feeling the benefits. When he plays like this, few players in the Premier League can match him.
Costa is another player who struggled to replicate his 2014/15 form last season, but, like Hazard, he is back with a vengeance under Conte. The 28-year-old's brilliant second-half strike was his eighth Premier League goal of the season, putting him top of the scoring charts ahead of Sergio Aguero and Romelu Lukaku.
"He's a brilliant player to have in your team when he's playing like today," said Neville in the Sky Sports commentary box. "He's a handful up front, and he defended three or four balls out of his own six yard box as well."
It's quite the transformation from last season. Costa is leading the line with tireless intensity again, and he's playing with confidence too. He has hit the target with 71 per cent of his shots compared to 53 per cent last season, and his conversion rate is up from 23 per cent to 33 per cent. He left the pitch to loud cries of "Diego, Diego, Diego" from the away end at St Mary's. Costa is back and he's lifting Chelsea.
The Kante-Matic partnership
Every title-winning side needs a strong central midfield pairing and N'Golo Kante and Nemanja Matic are certainly providing it for Chelsea. Kante was a force of nature in front of Leicester's back four last season, and he's now producing a similar level of performance for his new team.
He made more than twice as many interceptions (seven) as any other player on the pitch against Southampton, and he impressed with the ball, too, finding a team-mate with 92.2 per cent of his passes - a higher accuracy rate than any of his team-mates. It was a performance in keeping with his recent form.
Kante has injected energy and dynamism into Chelsea's central midfield, and Matic has impressed alongside him. The Serb struggled last season, but he is playing with authority again now, taking it in turns with Kante to run from box-to-box. There was one particularly impressive moment in the first half when he robbed Steven Davis high up the pitch before sending Costa through on goal.
Chelsea's powerful pairing have dominated the midfield in each of Chelsea's last four games. It's bad news for Cesc Fabregas, but Conte will be hoping it continues.
No European commitments
There were few positives to take from Chelsea's 10th-placed finish last year, but not having to juggle European commitments this season could help their cause. The Blues' new playing style demands high-intensity (they have outrun their opponents in each of their last three games) so the lighter load is especially beneficial.
It also gives Conte more time on the training ground with his players. "If you ask me if I prefer this situation, I don't, because Chelsea must be in this competition," he said back in August. "But because we are not, I will have a whole week to train with my players. That gives me a chance to work with them more compared to other managers in previous seasons."
The previous weekend of Premier League football was a good example of what can happen. Manchester City, Arsenal and Tottenham all failed to win after their midweek exertions in the Champions League, while Chelsea and Liverpool beat Manchester United and West Brom respectively after an uninterrupted schedule.