Newcastle boss Steve Bruce made two changes from the win at Tottenham last Sunday as Jetro Willems and Christian Atsu replaced Allan Saint-Maxim and the injured Matt Ritchie.
Watford boasted three changes from the 3-1 home defeat against West Ham as Jose Holebas, Etienne Capoue and Gerard Deulofeu made way for Christian Kabasele, Roberto Pereyra and Daryl Janmaat.
Javi Gracia’s Hornets had lost their opening three matches of the season, but were ahead in the second minute on Tyneside.
Abdoulaye Doucoure hit an effort from distance and the ball was deflected into the path of Will Hughes who slotted in Watford’s second-fastest Premier League goal past Martin Dubravka.
Andre Gray should have doubled Watford’s lead in the 15thminute, but he screwed his effort wide from six yards after being teed up by Pereyra.
Newcastle failed to create anything of note, but they did have a penalty shout ignored on 37 minutes when Willems felt he was fouled in the box, before there were some calls for handball which also fell on deaf ears.
However, they were on level terms four minutes later when a cross deflected down into the path of Schar and he took a touch before picking his spot past Ben Foster.
Newcastle started the second half in the ascendancy and Schar was inches away from scoring his second of the game with a free header which he sent just wide on 56 minutes.
Miguel Almiron then exchanged passes with Atsu but blazed his effort over the top from eight yards, before Foster pulled off a sublime save to parry Isaac Hayden’s effort over the top on the hour.
Isaac Success created problems for Watford when he came off the bench, while Pereyra was denied a winner by Dubravka four minutes from time.
At the other end, Yoshinori Muto was played in by Joelinton but slammed his effort wide of Foster’s upright as the sides had to settle for a share of the spoils.