But in failing to secure an outright victory — the first time that has happened since a city election law change two decades ago made the contest nominally nonpartisan — Emanuel has opened the door to a more competitive landscape. It is potentially a similar dynamic to that of presidential primaries, where a second-place finisher can gain more attention and resources than a top vote-getter who nonetheless underperforms.

At the very least, Emanuel enters the runoff with some tarnish on the aura of invincibility he had long sought to project, while Garcia’s progressive liberal challenge no longer seems quite the long shot it once did.

Despite his multimillion-dollar campaign war chest, Emanuel had trouble generating voter enthusiasm Tuesday. Turnout was exceedingly light across the city, and it may end up barely above the record low of 33 percent set in 2007 when then-Mayor Richard M. Daley won his sixth and final term.

With more than 98 percent of precincts reporting, Emanuel had grabbed more than 45 percent of the vote, with Garcia in second place at nearly 34 percent.