2009
He entered the qualifications of the 2009 Australian Open ranked #252. He beat Gary Lugassy (6–4, 6–3), Alex Bogdanović (6–3, 6–2) and Santiago Ventura (6–4, 6–1) to qualify for the main draw of the Australian Open for the second time in his career after a first round appearance in 2004. In the first round proper, he defeated #57 Steve Darcis in a gruelling 5-set encounter, finally prevailing 2–6, 6–3, 0–6, 6–2, 6–2. He was then beaten in straight sets by ninth seed and World No. 10 James Blake 6–3, 6–2, 6–3.
He then qualified for the SA Tennis Open in Johannesburg. In the first round, he upset third seed Marcel Granollers 7–5, 7–6(3) then defeated local wildcard Izak van der Merwe in a hard-fought 6–7(3), 7–5, 7–6(5) victory to reach the quarter-finals of an ATP tournament for the first time since February 2005 in Marseille.[2] There he was beaten by fellow Frenchman and eventual runner-up Jérémy Chardy 7–6(4), 6–3.
This loss marked the beginning of a period of struggle for de Chaunac, as he successively failed to qualify for the tournaments in Marseille and Indian Wells, while also recording a string of first and second-round defeats in Challenger tournaments. This period was highlighted only by a semifinal run at the Jersey Challenger in March and a final at a Futures tournament in Newcastle upon Tyne in May. The following week, he entered the qualifying draw for the French Open, discarding Grega Žemlja (3–6, 7–5, 7–5) and Pablo Santos (6–7(1), 6–2, 6–2), only to fall to Daniel Brands 7–6(5), 6–7(3), 10–8 in the qualifying round. He was equally unlucky at Wimbledon, losing to Alejandro Falla 6–4, 6–4, 6–4 in the last round of qualifying.
He bounced back, though, by qualifying for the next tournament in Indianapolis, where he put up a good but ultimately unsuccessful fight in the first round against Robby Ginepri, who prevailed 7–5, 5–7, 6–2, and went on to win the tournament. Two weeks later, he qualified for an ATP World Tour 500 tournament in Washington by defeating Brendan Evans 4–6, 7–6(3), 7–6(4). He beat Denis Istomin 6–4, 7–6(7) in the first round, before stunning fourteenth seed and World No. 32 Dmitry Tursunov 3–6, 7–6(3), 7–5, the highest-ranked player he ever managed to beat. Unfortunately, his run was cut short by American John Isner, who ousted him 6–2, 6–4 in the next round. As a result, he reached a new career-high, integrating the Top 150 for the first time. However, he failed to qualify for the US Open, losing to Marsel İlhan 7–6(4), 7–6(6) in the second round of qualifying.
A few weeks later, he qualified for yet another ATP-level tournament, his fifth of the year, in Metz, by beating Alex Bogdanović 6–1, 1–6, 7–6(7). In the first round, he pushed Ivan Ljubičić to a final-set tie-break, losing 4–6, 6–1, 7–6(1). His efforts were rewarded by a new career-high ranking of World No. 140.