"I Think I'm in Love with You" was more up-tempo than Simpson's previous singles and became a moderate hit. In the United States, the single debuted at number sixty-three on the "Billboard" Hot 100, on the issue dated July 1, 2000. Due largely on the strength of its radio airplay, the song peaked at number twenty-one in its seventh week and stayed on the chart for sixteen weeks. The single reached number five on "Billboard" Pop Songs and stayed on chart for twenty-two weeks. "I Think I'm in Love with You" was her first top five on the chart. Also achieved success on the Adult Contemporary and Rhythmic Top 40 charts. As the date, "I Think I'm in Love with You" sold 20,000 physical copies and has sold over 316,000 paid digital downloads according to Nielsen SoundScan.