The Argentina striker came off the bench on Saturday night to fire the Italian champions to a 2-1 win over potential title rivals Fiorentina, making it a perfect start to Juve's bid for a record sixth straight title.

"Higuain was very good and that goal was not at all easy to take," Allegri said.

"It was important for him and for the team. There are still a lot of areas we can improve in but I'm very happy with this test. We have made a much better start than last season and we have got three points in the bag."

Allegri is still struggling to work out his best line-up after overhauling his squad in the close season with the funds raised by Paul Pogba's world record transfer move to Manchester United.

By taking Higuain from Napoli and midfielder Miralem Pjanic from Roma and having signed Brazilian right-back Dani Alves, Allegri is widely seen as having put together a squad capable of challenging for Champions League glory as well as being runaway favourites to top the Italian league again.

Roma boss Luciano Spalletti admitted as much after his side produced a second-half blitz to beat Udinese 4-0 in their opener at the Stadio Olimpico.

"Everyone thinks that," Spalletti said with a smile. "But noone wants to just give up and accept this analysis. We all have to battle hard. It will be a pleasure to try to challenge them, precisely because they are strong."

Higuain had been left out of Juve's starting line-up because he is not deemed to be fully match fit.

Roma defensive crisis looms                  
                  
But he came off the bench to seal the three points with a strike that suggested his poacher's brain is as quick as ever, even if his waistline has expanded over the summer.

"I'm really happy to have made my debut, for the win and for the goal," he said.

"We have to carry on like this. It was really important to start with a win. We worked well and deserved the win."

Higuain, who was treated to a standing ovation in the Juventus Stadium, said he had been touched by the warmth of his welcome in Turin.

"I hope I can repay the affection with a lot of goals," he said. "I want to win as many titles as possible but there is a long way to go."

Fiorentina's Croatian striker Nikola Kalinic had cancelled out Sami Khedira's stunning first-half opener for the champions before Higuain killed the contest.

The 28-year-old, who scored 36 league goals for Napoli last season, had been on for exactly eight minutes and 27 seconds when Khedira's blocked shot spun across the Fiorentina goalmouth.

Higuain was first to react and he was able to squeeze the ball between Fiorentina goalkeeper Ciprian Tatarusanu and his near post from a tight angle.

Roma's 4-0 thrashing of Udinese was overshadowed by the sight of highly-rated Greek centre-back Kostas Manolas limping off injured three days before the second leg of the club's crunch Champions League qualifier against FC Porto.

Roma are favourites to advance to the money-spinning group stage after a 1-1 draw in Portugal in the first leg.

But Spalletti's defensive options are already limited as a result of Thomas Vermaelen being suspended after being sent off in the first leg.

Spalletti said taking off Manolas had been precautionary.

"His groin was giving him a bit of bother and there was no point in taking any risks, that is why we took him off."

Two second-half penalties from Argentinian midfielder Diego Perotti and late strikes from Bosnian striker Edin Dzeko and Egypt's Mohamed Salah secured Roma's win.