The Jambos started the current campaign with a 15-point deduction after going into administration and McHattie knows other clubs may expect them to struggle this term.
But, having eaten into the deficit already with an impressive derby victory, the left-back hopes the Gorgie outfit have what it takes to come through what could be a testing time on the park.
Speaking ahead of tonight's Scottish Premiership game at Partick, he said: "I think all the other teams in the SPL have kind of gotten us written off this season so hopefully we can prove them wrong.
"Each game is a cup final now. It will be a hard season but hopefully there will not be too many defeats.
"Partick will be a hard game but hopefully we can go there and show them how it's done.
"Sunday's game was magnificent. Everything about it - the fans, the occasion. It was great.
"But the result was the biggest thing, to get the three points. To win a derby was magnificent."
For McHattie, it was a week of stark contrasts, having contributed to the win over Hibs and then suffered a 6-0 thrashing at the hands of England with the Scotland Under-21s.
He said: "We were buzzing after Sunday and all the boys who were here this week are on a high and the ones who were away are a wee bit low.
"But as players we've just got to get through it. It's part of the game and we've got to learn from it."
Fans group the Foundation of Hearts were yesterday granted preferred bidder status by administrators BDO as they took a step closer to buying the troubled Jambos.
McHattie said: "We just focus on what's happening on the park and with training. But hopefully it can be resolved as soon as possible."
Bryan Jackson of BDO said: "The naming of a preferred bidder is the next step in the process of selling the club.
"It allows us to work with one party around which everyone can rally.
"In doing so, we maximise the prospects of agreeing a sale price that is acceptable to the Administrator of Ukio Bankas, and securing the necessary consent and ownership for FOH.
"This is an important milestone and reflects our belief that FOH is a credible bidder for the club.
"However, we all still have a lot of work to do to demonstrate to the major creditors that the bid can offer them the best possible outcome.
"Let's not get carried away - now is the time for everyone to get behind FOH to make this bid work."