By James Wong The Melbourne Rebels face the defending champion Highlanders at AAMI Park on Saturday night in what shapes to be the biggest challenge of their season so far. The Rebels are currently 3-1 and sit second in the Australian Conference after the first four rounds. Their three wins this season have come against teams that sit near the bottom of the competition ladder. The game against the Highlanders will be the first time this season the Rebels face a team that made the playoffs last year. "We're really looking forward to it. To be able to play against [them] and see where we're at against a quality opposition,” said Rebels coach Tony McGahan. Rebels captain Sean McMahon also said that his side was looking forward to testing themselves against the reigning premiers, who beat the Waratahs in Sydney last weekend. "Coming up against teams like the Highlanders you're always excited. They're the elite of the elite of the game and you look forward to getting up and playing