The two-year JGB yield fell 1 basis point to -0.015 percent, a three-month low. Investors took heart after the BOJ bought 2.5 trillion yen ($20.9 billion) of short-term bills in a regular debt-purchasing operation.
The central bank regularly buys debt from the market as part of its extensive quantitative easing scheme.
The benchmark 10-year yield dropped 2 basis points to 0.29 percent, its lowest since early February.
Giving JGBs a lift, Treasuries gained overnight after weaker US economic data rekindled doubts about whether the US economy is strong enough for the Federal Reserve to hike interest rates this year.
Uneasiness about Greece and its future in the euro zone have also underpinned safe-haven demand for sovereign debt like JGBs and Treasuries.