Cheshire Phoenix will have to overturn a 13-point deficit if they are reach their first BBL Cup final since 2010.
The Nix lost the first leg of their semi-final with London Lions 87-74 at the Cheshire Oaks Arena last night.
Cheshire held a three-point lead going into the final passage of play after winning the second and third quarters.
But London took control with a 13-1 burst and their superb shooting from range ensured they will start next Sunday's second leg at the The Copper Box with a commanding advantage.
The Lions netted five triples in the final quarter and 15 across the whole contest as they made 40% of their three-point attempts.
In contrast, the Nix drained only six of their 28 efforts from range.
Momcilo Latinovic (18 points) was the star of the show for the Lions, supported by Justin Robinson (17 points plus seven assists) and Jack Isenbarger (12).
But it was Cheshire's Robert Sandoval who led all-scorers with 24 points as well as contributing six assists. CJ Gettys (18) and Malcolm Riley (12) followed up.
The Nix had gone into the last-four clash on the back of an 87-59 BBL Championship win at Leeds Force on Friday.
