Hearts' last trip to Parkhead ended with their crestfallen players being bundled out of a chaotic Celtic Park and back on to the team bus in their strips and boots after watching their title dream die in the space of 11 crushing minutes. Meanwhile, the 800 Jambos in attendance - and the thousands back in Gorgie - were going through their own football trauma. The mere thought of ever returning to the home of the Scottish Premiership champions would have been a harrowing one. However, refreshed and reshaped, Wouter Vrancken's men are embracing the trip to face a Celtic side still failing to convince a support that are becoming increasingly disgruntled after another chastening European defeat at Benfica. Earlier this week, influential Hearts investor Tony Bloom repeated his faith in his title ambition for the Tynecastle club Sunday's fixture (15:00 BST) will give an indication as to whether or not that is likely to come this season. O'Neill defiant in defeat, but Celtic's 'flat-track bullies' fail another big test Celtic suffer fourth defeat in five against classy Benfica Late Nordsjaelland leveller denies Hearts winning start Vrancken wants 'fire to burn' in Hearts Despite the backstory to this weekend's encounter, Vrancken has demanded his side do not "live in the past". Meanwhile, Oisin McEntee, who was part of last season's squad, has insisted the trip to Glasgow is not a revenge mission. Versatile McEntee scored Hearts' opener against Nordsjaelland as they raised the curtain on their Conference League campaign, but they were served a late punch in the gut in the 1-1 draw . The Gorgie side have only won two of their past 11 away league outings, failing to keep a clean sheet in that period. However, last weekend's 5-0 win over St Mirren forms part of a run of five victories and a draw in seven matches under Vrancken after a challenging introduction to his tenure. Now with the opportunity to make a real statement early in his reign, the Belgian coach is urging his players not to dwell on May's heartbreak. "I'm convinced the players will be [focused] on the game on Sunday and not in the past," he said. "You can't live in the past. You have to move forward and look forward, and you have to take on the next one. "I hope the fire is there every game we play, and not only because something happened in the past. You also don't look in the past too much because it is negative energy, and we need positive energy. "This fire has to burn when you play every game, especially the top games." O'Neill views Hearts as genuine contenders Post-match in Lisbon on Thursday, Martin O'Neill expressed the emotions of a man who had just watched his team cruise to a 4-1 triumph. But the 74-year-old had just witnessed his side suffer a reverse of that, a fourth defeat in five games. The reason for the veteran manager's upbeat vibe was because of his players' response after crumbling in the first half of their Europa League loss to Benfica. The performance level from the Scottish champions improved and they could have scored more than the one goal they managed in the second period, though they were also fortunate not to have shipped more. Like last term, unrest between the fans and board is in the backdrop, but those same supporters are also growing restless at what they are watching on the pitch. Despite that, Celtic have still won 14 of their past 15 league games, scoring two or more goals in 11 of those. They have also won 26 of their past 29 home league games against Hearts, although have lost two of their last six. Last term, Hearts picked up seven points in four league games against Celtic - the most by any non-Old Firm side in a single campaign since the 1999-00 season. O'Neill believes Hearts are genuine contenders again and is anticipating a match that will be as challenging as May's dramatic title decider. "I think it will be every bit as tough as it was on the last day of last season," the Celtic boss said. "I genuinely do [think they are title challengers]. I know they've lost two [league] games, but overall, I do, I think they can challenge."