Nine days before the draft itself Sidney found out that Pittsburgh Penguins had won the lottery and they would draft Sidney as number one as everyone had expected. This gave Sidney the opportunity to play with his idol Mario Lemieux. Sidney signed a contract worth about 10 million for a three year deal, this dream contract also had some very attractive bonuses.

It was here in the beginning of the season people gave him the nickname "Sid the kid". Playing in his first ever NHL game he faced the New Jersey Devils, which was known for playing exceptionally well defense. Unlike his big idol Mario Lemieux, Sidney didn't get a goal in his first game, although he had a great opportunity but was robbed by star goaltender Martin Brodeur. He did manage to get an assist on Mark Recchi's goal that night. The next game the Penguins were facing Carolina Hurricanes, here he made a phenomenal pass to Ziggy Palfy who scored the game tying goal. But Sidney had to wait for his own goal until the third game against Boston Bruins on October 8 2005, In front of a sellout crowd in Pittsburgh he scored a great goal as well as getting 2 assist making him the number one star of the game despite Penguins loosing the game.

At the end of October Sidney was named rookie of the month with 2 goals and 12 assists beating Alexander Oveckin who had 13 points during the same time.

Even though Sidney were putting up great numbers and meeting the big expectations Pittsburgh Penguins were struggling big time, loosing their first 13 games of the season. This resulting in replacing head coach Ed Olczyk with Michel Therrien. Michel made Sidney alternative captain, he also made some big changes to the lineups and made Sidney play center instead of rightwing as he had been doing since the start of the season. This helped Sidney to start score goals more regularly and Penguins were starting to win games.

As things were finally starting to look brighter for Sidney and the Penguins worst possible scenario happened. On December 8 against Buffalo Sabres, Mario Lemieux was diagnosed with an irregular heartbeat and was forced to retire. As expected this had a bad effect on the team and it had trouble winning games again.