A loss to Sydney FC could drop the Phoenix to as low as fourth where they would host a playoff game in the first week of the finals before having to go on the road if they were victorious. A top-two finish is the desirable outcome.
"I think it's pretty crucial because history shows no-one's won the grand final from outside the top two," Merrick said. "I'm not saying that can't be changed if we finish outside the top two but it's obviously a huge advantage. So we are pretty keen to get in the top two."
Melbourne Victory look likely to secure the Premiers Plate during what shapes as an exciting round of matches to finish the regular season.
The Phoenix got their groove back on Friday night with a last-gasp 3-2 win over the Central Coast Mariners at the Cake Tin.
Merrick's side had to overcome a two-goal deficit but a late double to substitute Kenny Cunningham, and an earlier strike from Roly Bonevacia, gave the Phoenix three valuable competition points.
There were no injury concerns to emerge from the win over the Mariners, although midfielder Michael McGlinchey didn't train today due to a virus, while regulars Ben Sigmund and Alex Rodriguez were also given a rest.
Merrick is unlikely to make many changes for Sunday's match and he said they were appreciative of a nine-day turnaround between games.
"There's a lot of players fighting for their position and that's the way it should be."
Meanwhile, a report from across the Tasman has linked Nathan Burns with a move away from the club next season. The striker, who has scored 13 goals during a strong campaign for the Phoenix, is believed to have an out-clause in his contract and SBS website The World Game suggested he would depart.
Merrick didn't want to buy in to any speculation around Burns who was linked with a Chinese club during the transfer window earlier this year.
"Our focus is purely on a key game at the end of the season against Sydney and our finals games and we are not going to be distracted by any other talk," Merrick said.
