The Magpies have lost 2-1 to Tottenham Hotspur, Chelsea and Manchester City, who all finished in the top five last season and are already in the top five this term.
Rafa Benítez's side also drew 0-0 with newly-promoted Cardiff but find themselves in 18th place in the fledgling table ahead of a free weekend as the top flight campaign pauses for an international break.
But Dúbravka insists that United have acquitted themselves well in each game and told nufc.co.uk: "I don't agree if anyone says we are not in a good shape.
"We've played against very tough opponents and in all of the games, they were very close and we've missed a little bit of luck, especially against Tottenham.
"We could easily have taken a draw against Chelsea and unfortunately we didn't win against Cardiff, but we created chances and stood compact, and if we play like we did against Manchester City - especially in the second half - we can be successful.
"We hoped that we could change something (after falling behind for the second time); we tried to stay focused for the full 90 minutes, but of course it's difficult when you play against Man City at their stadium.
"It was a tough game but it showed that we have brilliant players ourselves and we have confidence for the next games."
Dúbravka is currently on international duty with Slovakia. He was an unused substitute in Wednesday's 3-0 friendly win against Denmark, but is expected to start against Ukraine in the UEFA Nations League on Sunday.
Slovakia narrowly missed out on qualification for the 2018 World Cup, finishing second to England in Group F, but the Newcastle goalkeeper is hoping to help his country reach the European Championships in 2020.
And he said: "Every time when I go to the national team, I really look forward to seeing my team mates and the coaching staff. It's great, the mood there - the same as at Newcastle.
"I really hope we will play the same football as we have been recently. I think we have a quality team, which we've shown in previous games.
"We have been together for the last ten years so that's important, and we've brought through some quality young players who bring with them extra energy."
