Huddersfield coach Paul Anderson accused his team of failing to live up to expectations after slipping to defeat at Widnes.
Joe Mellor and Rhys Hanbury scored in the closing minutes at the Select Security Stadium as the Vikings recovered from 20-12 down to snatch a 22-20 win in the First Utility Super League.
It was another worrying capitulation for the Giants - last year's League Leaders' Shield winners - after relinquishing a 24-6 advantage to draw with Hull KR last week.
Anderson said: "We got outfought. Widnes worked hard and got everything they deserved.
"Once again we made some things look easy and some things look very hard. Our concentration and attention has to be better - all round we have to improve.
"There is a level of expectation around Huddersfield at the moment which we are failing to live up to. We have got to make sure we respond to that.
"We probably need to do some practice closing games out. There was a little bit of indiscipline with regard to our systems. We have got to make sure we get a response."
Anderson had no issues over Hanbury's winning try, awarded as he touched down amid a swarm of players after Jack Owens was tackled close to touch.
He said: "He gave a try - no complaints from me."
Widnes coach Denis Betts felt his side thoroughly deserved their victory after a hard-working performance.
Betts said: "It is a fantastic win. We were missing some players but we have been working really hard and have just beaten a side that beat us quite convincingly last year.
"There is a great team spirit, great work ethic and belief. One thing we really had to work hard on was our commitment to defence.
"It takes a couple of years to get to this stage and against a very good attacking team - there are some talented individuals in that team - it was a pretty impressive performance tonight.
"The confidence they can get from that is immeasurable."