Sporting Kansas City and the Houston Dynamo battled to a goalless draw on Saturday in a hard-fought first leg of Major League Soccer's Eastern Conference championship tie.
The sides will have it all to play for in the second leg at Kansas City on 23 November.
The winners will play the Western Conference Champions in the MLS Cup final on 7 December.
The Western Conference final begins on Sunday when Real Salt Lake host the Portland Timbers.
Portland beat Seattle in the conference semi-finals, while Real Salt Lake ousted two-time defending champions the Los Angeles Galaxy.
Houston went into their third straight conference finals after shocking the New York Red Bulls - top seeds in the East and winners of the Supporters' Shield as the club with the best regular-season record - in the conference semi-finals.
They looked to have struck early, but Kofi Sarkodie's 18th minute effort was ruled offside.
Ten minutes later Houston's Boniek Garcia curled a free-kick toward Sporting's goal but keeper Jimmy Nielsen made the save.
Quality chances were few for both teams, who were showing the effects of playing on short rest.
Both played extra-time matches on Wednesday and travelled cross-country on Thursday.