The current two-leg conference semifinal playoff format was adopted in 2003.
Between then and 2009, there have been 28 home-and-home Conference Semifinal playoff series. In the first legs of those series, there have been nine draws, meaning 19 first-leg matches have ended with a winner and a loser.
Of those 19 winners, 10 have advanced, while nine of those results have been overturned in the second leg. In other words (or numbers), teams with a lead heading into the second leg have gone on to advance 53 percent of the time.
However, of those nine overturned results, eight of them occurred following a win by the home team in the first leg. Only once has a team that lost the home leg gone on to win the away leg and the series.
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What does all of this say about this year?
This year is the first time since 2006 that all four conference semifinal series have a leader after the first leg. FC Dallas, the LA Galaxy, New York Red Bulls and Colorado Rapids all carry a one-goal advantage heading into the second leg.
Odds are that two of these four will not maintain their lead this weekend. Colorado and FCD, who won their home legs (and now hold a slim one-goal lead), are the most likely candidates to capitulate.
Meanwhile, New York and LA, each playing at home in the second leg and each carrying a one-goal lead, have an overwhelming chance of advancing. Of the six times that a team has won the away first leg, they have come home and advanced five times.