United make the long trip to Stamford Bridge at the weekend (kick-off 3pm BST) in the search of back-to-back victories for the first time this term.
Although Chelsea sit in fifth place under manager Frank Lampard, netting 14 times in their previous five league outings, but Lascelles admitted confidence is high ahead of the Magpies' away encounter against the Blues following a much-needed win against Manchester United.
He said: "They're a young side with not much experience in there. We've been working really hard this week and we're looking forward to it. It's going to be a tough game but we do fancy our chances.
"We're still going off the last game. We beat Man United at home and there's no reason why we can't beat Chelsea. We've still got the confidence from the last game and hopefully we can go and do the same job."
After disappointing defeats to Norwich City and Leicester City, the Magpies have responded positively on both occasions with 1-0 victories against Man United and Tottenham Hotspur.
Lascelles believes the impressive wins against teams competing in Europe this term brings satisfaction as United aim to build on their current league position of 16th, one point above the relegation zone.
"It's not very consistent but it is pleasing that we can beat these big teams," the 25-year-old added. "Over the course of the season, the games we have been losing to teams like Norwich, we need to sort that out but it gives us confidence that we can beat these big teams and playing Chelsea at the weekend, we are full of confidence going into that.
"The manager has drilled into us about a game plan. Both times against those teams, it has worked. It's about sticking to the game plan and giving it our all. Both of those games, we were fiery and really passionate.
"I think that's always how we need to play whereas against Brighton and Norwich, it wasn't the same. We need to play with the same energy levels, heart and aggression as we did against Man United and Tottenham."
Matty Longstaff will be hoping to maintain his place in United's starting eleven this weekend after a memorable Premier League debut against Manchester United in which the Newcastle-born teenager netted a wonderful match winner at St. James' Park.
And Lascelles expressed his delight for the 19-year-old and is eager for the midfielder to carry on from where he left off against the Red Devils.
"From the first minute of pre-season, he's been one of our best players in training," Lascelles said. "He's a really nice lad - genuine and humble. Of course, he's a young, Geordie lad so it means the world for him to play for Newcastle so I couldn't be more happy for him. Him and his brother have done a fantastic job and hopefully it continues."
