If we see Juventus records during knockout phase they actually had impressive records and since playoff matches until quarterfinal Juventus has several times to win at their opponents home ground with cleansheet status and besides that Sporting also doesn't too strong at their home because according to their records Sporting has been lose several times on champion league group stage so in my opinion Juventus had good opportunities to gets at least draw results at Sporting home and advance to semifinal match
I don't think the sporting team is weak. I saw Sporting's performance against Juventus in the away match as well. Sporting players performed well. Sporting played more attacking than Juventus. Even then, they could not break the defense of Juventus. On the other hand, I think the Sporting team will be more confident in the home match. Their performance will be sharper in the second leg. So I find it very unlikely that the Juventus team can easily beat the Sporting team.
Sporting is not weak at all, they win the game against Arsenal Arsenal is the first team in the premier league and they had a good performance against the first Juventus. The 1-0 result is not bad for Sporting because they can still have the chance to beat Juventus and pass this stage however, Juventus is not a team to let Sporting have any chance in this game.
Since Juventus beat Sporting 1-0 in the first leg, Sporting will try to beat Juventus in the second leg. However, if Sporting implements a great strategy, I think they will be able to overcome this goal difference and secure victory.