April 9 (Reuters) - Investments in U.S. bond funds surged to their highest level in nine weeks in the week ended April 7, helped by a retreat in bond yields, which saw a strong rally in the first quarter. U.S. bond funds saw $13.7 billion in inflows, the most since the week ended Feb. 3, Refinitiv Lipper data showed. This inflow was mainly driven by U.S short- and intermediate-term investment-grade funds, which had net purchases of about $5.1 billion, the biggest in seven weeks. Treasury yields fell this week on investors’ view that market pricing based on an earlier-than-expected tightening by the Federal Reserve was too aggressive. U.S. equity funds received $2.7 billion worth of inflows, as the S&P 500 index and the Dow Jones index hit record highs this week, buoyed by strong jobs and service sector data. U.S. growth funds, which hold most of the high-flying technology-related stocks, attracted inflows of about $1.35 billion, boosted by a drop in bond yields. Tech funds in particular received $1.15 billion, bolstered by an increase in global demand for chips and semiconductors. U.S. value funds, on the other hand, received inflows of $226 million, the lowest in five weeks, the data showed. Meanwhile, U.S. money market funds saw $8.05 billion in outflows after massive inflows in the previous two weeks.