While working on MVC5 application, I faced this issue, I was using Ajax.BeginForm() and from controller, I was returning content result. But instead of updating the DIV, the content was opened in new Tab. Initially I thought it was due to some javascript error, but it was not working with Ajax.ActionLink also. Later I found it was due to missing “Microsoft.jQuery.Unobtrusive.Ajax” package. You can install this via NuGet.

And include it in the BundleConfig.cs.

bundles.Add(new ScriptBundle("~/bundles/jqueryunobtrusive").Include(
            "~/Scripts/jquery.unobtrusive*"));

And include the jqueryunobtrusive in _layout.cshtml file.

@Scripts.Render("~/bundles/jqueryunobtrusive")

It will resolve this issue.

Happy Programming :)