United started their first campaign back in the top-flight with two defeats, and endured a run of just one point from nine games stretching from late October to late December.
But the players, manager, staff and supporters stuck together throughout the tough times and the Magpies' form in 2018 was enough to see them not only climb away from the bottom three but eventually break into the top half of the table.
And defender Clark told nufc.co.uk: "If you'd offered us that at the start of the season, a lot of us wouldn't have believed it to be honest.
"We knew it was going to be tough coming into the season. We obviously believed in our ability, but to finish in the top ten at the end of it was unbelievable. It's been a massive effort throughout the whole club - not just the players on the pitch but the staff, all around the ground and all around the training ground, and everyone involved with Newcastle.
"The fans have travelled home and away and it's been a massive help to everyone. The support was unbelievable and it was a massive club effort."
The Republic of Ireland international scored a vital goal against West Brom in November as United came from two goals down to earn a vital point during their worst run of the season.
And he insisted: "We always believed in our ability; sometimes we went through rough stages and tough spells but we always believed we'd come out of it and turn it round by keeping doing what we were doing and what we were practising on the training pitch.
"Everyone put a massive effort in. It was a long season but it's where we wanted to be - to be in the Premier League, playing against the best teams and best players in the world.
"It was up and down but our aim was just to get as many points on the board as possible and compete against the teams that were around us. We managed to do that and we finished up in tenth place, which was unbelievable for us.
"The aim now is we want to improve on what we've done. Hopefully we can do that next season, but everyone right now is enjoying their break and looking forward to coming back and cracking on again."
