An Elabe survey of voter intentions taken before the shooting on the Champs Elysees shopping street in central Paris showed Macron in front and far right leader Marine Le Pen falling further behind him.
But even leaving out the potential impact on voter sentiment of the latest deadly attack in a series that has hit France in the past two years, neither was totally assured a spot in the May 7 runoff round.
Two other candidates were snapping at their heels.
The poll was conducted on Wednesday and Thursday - before the shootout in which the attacker also died and two other police officers were injured.
The attack was swiftly claimed by militant Islamist group Islamic State.
Le Pen has made immigration and security a core part of her campaign.
She wants to tighten French borders controls and build more jails, and says authorities are not doing enough to protect citizens from attacks like Thursday's. Such attacks have claimed more than 230 victims in France since January 2015.Read more at Reuters