During what Championship was the Opponent Jeff Borowiak?
CREATE TABLE "singles_18_8_titles_10_runner_ups" (
  "outcome" text,
  "date" real,
  "championship" text,
  "surface" text,
  "opponent" text,
  "score" text
);
SELECT "championship" FROM "singles_18_8_titles_10_runner_ups" WHERE "opponent"='jeff borowiak';