Sydney/Perth, Jan 1 : Led by Stefanos Tsitsipas, Greece make their debut in the United Cup at Sydney on Tuesday while World No.1 Novak Djokovic's Serbia will close out the proceedings in Perth against the Czech Republic, hoping to win the match and clinch a berth in the quarterfinals of the mixed teams tennis tournament being played in various venues in Australia. Greece make their 2024 debut at the United Cup in Sydney during the Tuesday day session, with Top 10 stars Maria Sakkari and Tsitsipas presenting a big obstacle in Chile's quest to stay alive in the tournament. Having dropped their first Group B tie to Canada, Chile will be hoping that Daniela Deguel can pull a big upset against World No. 8 Sakkari and that Nicolas Jarry, at a career-high No. 19 in the ATP Rankings, can topple last year's Australian Open finalist Tsitsipas. In the evening session in Sydney, the Netherlands will look to clinch victory in Group F when they play Croatia, which suffered a narrow defeat to Norway on Monday. Tallon Griekspoor will look to kickstart the Dutch charge against Borna Coric in the opening match before Arantxa Rus looks to upset Donna Vekic in the WTA singles. In Perth, in the final group stage match, Serbia have the opportunity to win Group E should they beat the Czech Republic. World No. 1 Novak Djokovic, who won both his singles and mixed doubles with Olga Danilovic, again holds the key to the team's chances, as he takes on Jiri Lehecka in a first-time ATP head-to-head meeting. A country's position within its group is determined by number of ties won and ties played. If three teams are tied with the same number of tie wins, then the team having played fewer total matches (singles and mixed doubles) will be eliminated and the winner of the head-to-head matchup between the two remaining teams advance. If still tied then the following procedures decide the group order: the most match wins (singles and doubles), then the highest percentage of matches won, then the percentage of sets and then games won. Determination of best runner-up quarterfinal spot: the number of ties won; the number of ties played. In a tie between three teams, the team having played fewer total matches (singles and mixed doubles) will be eliminated and, if still tied then the team with the most match wins (singles and doubles). If still tied then the following procedures decide: the highest percentage of matches won, the highest percentage of sets won, the highest percentage of games won. /IANS