The Magpies were looking to spring a surprise at Stamford Bridge on Monday night in the Premier League, but conceded twice before the break to leave themselves with a mountain to climb.
Timo Werner laid on Olivier Giroud for the first goal in the 31st minute before then breaking his 14-game goal drought by netting Chelsea’s second in the 39th minute.
Newcastle had no answer, but did not concede in the second half and Lascelles feels they can take the positives from the second 45 minutes at Chelsea as they did not fold and suffer a heavy loss.
The Magpies star said post match on Sky Sports: “I just think we did not start well enough.
“From our goal-kick we kicked it out for a throw in and that set the tone.
“We need to realise we should not need to go one or two down to get going.
“We were off them a bit and made it easy.
“Against a team like Chelsea you have to be nasty and if you don’t do that their quality will come through.”
And Lascelles added: “The performances have been better but tonight was not good enough, especially the first half.
“We did not give up in the second half and those positive signs are always good to have.”
Newcastle continue to sit fourth from bottom in the Premier League and boast a seven-point advantage over third bottom Fulham.
However, Fulham beat Everton 2-0 at the weekend, have only lost one of their last five league games, and have a game in hand on Newcastle.