The survey indicates Brown holds a razor-thin 45 percent to 43 percent lead over Warren among likely voters, well within the poll’s margin of error of plus or minus 4.1 percentage points. Brown’s lead evaporates, with 47 percent for each candidate, when voters who are undecided are asked which candidate they are leaning toward.

The poll is a reversal from a September Globe survey that showed Warren ahead 43 percent to 38 percent, as well as several other recent polls that have found Warren with a slight lead. The shift underscores the belief long held by both sides that the race, active for more than a year, would be competitive until the end…

The poll comes a day ahead of what is supposed to be the candidates’ fourth and final debate, scheduled for Tuesday evening. Debate sponsors, a media consortium including the Globe, have not made a decision whether to postpone or cancel the debate, as the full effects of Hurricane Sandy on the region are not yet known.