Kod:
private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Right & dataGridView1.RowCount>0)
{
var hti = dataGridView1.HitTest(e.X, e.Y);
dataGridView1.ClearSelection();
dataGridView1.Rows[hti.RowIndex].Selected = true;
}
}