Newcastle boss Rafa Benitez watched his side go down 1-0 at Fulham and then described it as a "wake-up call".
The Magpies were beaten by Matt Smith's first-half header in a lacklustre Championship season opener following summer spending of almost £45 million.
Benitez knows Newcastle cannot afford many similar performances if they are to immediately return to the Premier League.
"I'm really disappointed because we did not play at the level we expected," he said. "We did not win the ball too much in the second ball and were not keeping the ball properly. We were not concentrating. This game could be a wake-up call for everyone.
"The only positive is it is the beginning of the season and we can wake up. At least everyone has to realise it has to be like this for the rest of the season.
"We didn't play at the level we want to play and have to play if you want to score goals and win games. You have to be much better. We have to realise this is a tough competition and we have to be much better."
Newcastle had two penalty appeals waved away for handballs by Ryan Tunnicliffe and Tomas Kalas but Benitez refused to criticise referee Simon Hooper.
"The first one was clear and not given," he said. "The second one depends on the referee."
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Tim Krul has hinted hew could play a part in Newcastle's fight to regain their Premier League status at the first attempt.
The 28-year-old goalkeeper could only watch from afar as the Magpies slipped out of the top flight after suffering a season-ending knee ligament injury while on international duty with Holland in October.
Krul is not the only Newcastle keeper to suffer misfortune this season, with deputy Rob Elliot having also been struck down by a knee ligament injury, leaving third-choice Karl Darlow in goal for the final eight games of the campaign.
Club officials are currently working to persuade Rafael Benitez to remain as manager amid speculation that many of the bigger names with whom he has worked in recent weeks will leave the club this summer.
However, having watched the club's remarkable 5-1 final day victory over Tottenham, Krul appears to be ready to roll up his sleeves and get down to work once again.
Yesterday was a great result for the club in what has been an otherwise incredibly frustrating and disappointing season both for the club and me personally.
I am still finding it hard to come to terms with what has happened this season, and it's been devastating for me that I haven't been able to help us sustain our Premier League status due to injury.
On a personal level, over the past week or so I have been making big strides in the right direction by training outside with the physio and goalkeeping coach as I continue towards full fitness.
The fans have been incredible and deserve success. Everyone at the club will be fighting to get Newcastle United back into the Premier League where it belongs.
Newcastle manager Rafael Benitez admitted it would be tough for him to leave the club following the final-day 5-1 Premier League win over Tottenham.
Benitez's name was chanted throughout the game as his side produced one of their best performances of the season despite being reduced to 10 men midway through the second half, consigning Spurs to third place in the process.
Newcastle owner Mike Ashley watched the game from the directors' box for the first time this year and then held talks with the Spaniard after the final whistle with a number of other big clubs already being linked with a move for Benitez.
The former Real Madrid boss admitted his rapturous reception would make it harder for him to decide to walk away as he continues to consider his options.
I was expecting the fans to get behind the team and support me but it has been amazing. I was open to talk and now I am more open to talk.
It is not easy to leave a club like this and I will talk and analyse and try to do the best for me and the best for Newcastle United. It has got to be the best for both.
We are really disappointed because we couldn't stay up, but really happy that we gave the fans something to enjoy today. Since I've been here in terms of effort and hard work you can say nothing (negative) about these players.
A message from Sunderland fans mocking Newcastle's relegation is set to be flown over St James' Park when the Magpies face Tottenham there on Sunday.
The Black Cats secured their Barclays Premier League safety and condemned north-east rivals Newcastle to the drop with Wednesday's 3-0 victory over Everton at the Stadium of Light.
On Saturday aerial advertising company Air Ads posted a message on Twitter which said: "Busy afternoon, putting together a banner for St James Park tomorrow afternoon!"
That was accompanied by a picture of a banner being prepared, with red letters across it spelling out 'AUF WIEDERSEHEN PREM'.
It comes after a crowdfunding page was created on gofundme.com on Thursday by 'SAFC AWAY DAYS', with the stated aim of the project being to "organise a fly past banner over St James' Park to allow us to say bye to our neighbours for a little while".
Four donations have been made, with an anonymous one of just over £1,000 accounting for virtually the whole of the total amount raised. The page says £900 will be for the aircraft trailing the banner, with the rest going to charity.
Andros Townsend has revealed the free-kick which hauled Newcastle out of the relegation zone was honed on Tottenham's training pitches.
Just a few months ago, the 24-year-old England international was out of favour at White Hart Lane and training with the second team, although all the while, he was awaiting his next chance.
That came when the Magpies invested £12million in his services in January, and his most telling contribution yet came on Saturday when he smashed a 58th-minute free-kick past Crystal Palace keeper Wayne Hennessey to clinch three priceless points.
Townsend said: "At the back end of last year, I used to stay out for hours practising free-kicks, left foot then right foot.
"It was frustrating, but all that hard work on the training field eventually pays off. It paid off in dividends against Palace - in front of 52,000 fans."
It was Townsend's fourth goal in 11 appearances in a black and white shirt and his third in the last five, but it was by some distance the most important yet.
He said: "I have scored goals when we were 5-0 down and 3-0 down, then a third goal in a 3-0 win against Swansea. But this is what you live for, moments like this when your team really needs it.
"I'm glad to repay the faith and hopefully in the last two games, I can contribute with more goals and assists."
Townsend and his team-mates have two games left in which to secure what just a few weeks ago looked like an unlikely escape, and they know they may have to win both - away to relegated Aston Villa and at home to high-flying Tottenham - if they are to survive.
However, with relegation rivals Sunderland and Norwich both having a game in hand, even that may not prove enough during what is sure to be a dramatic conclusion to the campaign.
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