Two more last night (6/11): the Rangers' Yu Darvish tossed a six-hit, ten strikeout whitewash against the Miami Marlins at home in Arlington, and in Seattle, the Yankees' Masahiro Tanaka improved his record to 10-1 and kept his floundering team within striking distance in the AL East (and in the terminally crowed "wild card" race) with a six-hitter in New York's 4-2 win over the Mariners. (Ex-Yank Robinson Cano spoiled Tanaka's shutout in in the ninth inning with a one-out, two-run homer.)
A little more research will be required to determine if this is the first instance of two Japanese pitchers throwing complete games on the same day. We'll get back to you on that a bit later, but what we can say is that this most recent incarnation of Japanese starters has easily been the most successful.
As of today, Tanaka and Darvish have a combined record of 17-3, and without them their two teams would likely be a good bit further down the standings.