Places to Play: Oi Sports Center (Shinagawa - Tokyo Metro)
 
These 14 tennis courts are part of a larger park / recreation complex run by the Tokyo Metro government, on one of the manmade islands in Tokyo Bay, past Shinagawa station and east (bay-way) of the Oi horserace track.   There is also a park, several baseball fields, gateball, athletic track, etc.
 
Twelve of the courts are hard surface and 2 are clay.  Of the hard courts, 6 have lights for evening play.
 
Hours of use are:
- from April 1 to Oct 31, 9 AM to 6 PM, and on to 9 PM for the lighted courts;
- from Nov. 1 to Jan. 31, 9 AM to 4 PM;
- from Feb. 1 to March 31, 9 AM to 5 PM. 
Usage on weekdays is generally in two-hour blocks; usage on weekends is in 3 to 4 hour blocks (such as 9 AM to 1 PM, 1 to 5 PM, 5 to 9 PM). 

Usage is through the Tokyo Metro lottery system, which is described in a separate listing.

The address is Yashio 4-1-19, Shinagawa-ku, and admin office phone is 3790 2378.   The location is just to the east (bay-ward) of the Oi horserace track.

Getting there by car (your own or taxi) is easiest/fastest.  A fairly straightforward path is to get on the Dai-Ichi Keihin route (also know as route 15) that passes in front of Shingawa station, follow this south (towards Yokohama) about 3.5 kilometers from Shinagawa station, then turn left (bay-ward) at the Minami-Oi-Ichi intersection.  Follow this straight about a kilometer, passing under an expressway and over a short bridge.  At the first large intersection past the bridge, turn right and you are in the park.  The courts are in two separate clusters; the admin office is at the cluster closer to the baseball fields.  (By the way, other intersections before and after the Minami-Oi-Ichi intersection will also get you onto the island.)

The closest train is the monorail going to Haneda airport; get on this at Hamamatsu-cho station and get off at Oi Keibajo-mae (the horserace track) and walk 5 to 10 minutes across the bridge onto the manmade island.