A more competitive NL Central in 2011

Here's an article by Anthony Castrovince about competitiveness in the NL Central in 2011. Castrovince writes that with two non-contending teams from 2010 (Brewers, Cubs) making major moves to improve their clubs (Greinke and Marcum, Garza), what on paper looked like a two horse race between the Cardinals and Reds in 2011 may instead turn out to be one of the most competitive divisions in baseball.

Today's trivia question: What was the most recent year in which the winner of the NL Central division was not decided until the final weeks of the regular season?