Serena, a 23-time Grand Slam singles champion, makes her 21st appearance at the US Open after telling the world that she will soon be "evolving" out of tennis and into the next stage of her life.
Vice-captain De Silva hit 109 and put on 82 runs for the eighth wicket with Ramesh Mendis, who was unbeaten on 45, after the hosts resumed day four on 176-5 in Galle.
