2006–2009 Lertcheewakarn started playing her first ITF Circuit events in August 2006. She made her
WTA Tour main-draw debut in 2007 as a qualifier, defeating world No. 97,
Melinda Czink of Hungary, in straight sets in the final qualifying round, before losing to
Aiko Nakamura in three sets in the first round. In May 2008, Lertcheewakarn won her first pro title in singles at $25k Balikpapan, defeating the top seed
Isha Lakhani of India, in straight sets. In 2009, Lertcheewakarn received a main-draw
wildcard into the
Pattaya Open; she lost her first-round match against
Shahar Pe'er, which lasted 52 minutes, 1–6, 0–6.
2010 She received a wildcard to
Pattaya Open, but lost in the first round to
Chanelle Scheepers, in a two-hour-and-forty-minute three-set match in which Lertcheewakarn had a 4–1 lead in the second set. She then received a wildcard to the
Malaysian Open where she beat
Ksenia Pervak in the first round in straight sets, making this her first WTA main-draw win ever. At the $50k Nottingham Trophy, she advanced into the quarterfinals, before losing to
Elena Baltacha in two straight sets. Lertcheewakarn received a wildcard entry to the
Wimbledon Championships where she was defeated by
Andrea Hlaváčková in the first round. She ended the year inside top 200 in singles and doubles.
2011 Lertcheewakarn qualified for the
Auckland Open but lost to
Heather Watson in the first round, 1–6, 1–6. At the
Malaysian Open, she defeated
Alberta Brianti, 6–4, 2–6, 6–2, and lost to a qualifier
Anne Kremer in the second round. In doubles, Lertcheewakarn reached a
WTA tournament final, partnering
Jessica Moore, they lost to
Dinara Safina and
Galina Voskoboeva in a close match. She lost in the first round of the
Baku Cup to
Ksenia Pervak, having led 5–3 in the third set. At the
US Open, Lertcheewakarn qualified for her second Grand Slam main draw, defeating
Zuzana Kučová,
Ashley Weinhold and
Kristýna Plíšková in three tough matches. In the first round, in just her second Grand Slam tournament, she lost to
Anastasiya Yakimova 0–6, 6–4, 3–6. Lertcheewakarn won the
Al Habtoor Challenge, beat
Bojana Jovanovski,
Regina Kulikova,
Simona Halep and
Kristina Mladenovic en route. She also qualified for
HP Open but lost to
Samantha Stosur in three sets, she was two points away to score the victory. In 2011, Lertcheewakarn broke into top 100 in doubles and top 150 in singles.
2012 She reached the final of the $50k event in
Gifu but lost to
Kimiko Date-Krumm, in three sets. She qualified for the
Birmingham Classic main draw, defeating
Sesil Karatantcheva en route. In the first round, she lost to
Misaki Doi in three sets. At the
Stanford Classic, Lertcheewakarn lost to
Nicole Gibbs, 4–6, 4–6.{{cite news| url= http://timesofindia.indiatimes.com/sports/tennis/top-stories/Success-for-younger-Radwanska-in-Stanford/articleshow/14819599.cms| title= Success for younger Radwanska in Stanford ==WTA Tour finals==