The Estoril Open (also known as the Millennium Estoril Open for sponsorship purposes) is an ATP clay court tennis tournament held in the Portuguese Riviera. The event takes place at the sports complex of Clube de Ténis do Estoril in Cascais. The tournament was removed from the 2025 ATP calendar, and its future was left uncertain, until it was announced in September 2024 that it would be returning in 2025 as a Challenger 175 event.

Estoril Open was created by former Dutch tennis player Benno van Veggel and Portuguese football agent Jorge Mendes in 2015 to replace the Portugal Open, which was canceled due to lack of sponsorships.

Year	Champion	Runner-up	Score
2015	Richard Gasquet	Nick Kyrgios	6–3, 6–2
2016	Nicolás Almagro	Pablo Carreño Busta	6–7, 7–6, 6–3
2017	Pablo Carreño Busta	Gilles Müller	6–2, 7–6
2018	João Sousa	Frances Tiafoe	6–4, 6–4
2019	Stefanos Tsitsipas	Pablo Cuevas	6–3, 7–6
2020	Not held due to the COVID-19 pandemic.
2021	Albert Ramos Viñolas	Cameron Norrie	4–6, 6–3, 7–6
2022	Sebastián Báez	Frances Tiafoe	6–3, 6–2
2023	Casper Ruud	Miomir Kecmanović	6–2, 7–6
2024	Hubert Hurkacz	Pedro Martínez	6–3, 6–4

Year	Champions	Runners-up	Score
2015	Treat Huey Scott Lipsky	Marc López David Marrero	6–1, 6–4
2016	Eric Butorac Scott Lipsky	Łukasz Kubot Marcin Matkowski	6–4, 3–6, [10–8]
2017	Ryan Harrison Michael Venus	David Marrero Tommy Robredo	7–5, 6–2
2018	Kyle Edmund Cameron Norrie	Wesley Koolhof Artem Sitak	6–4, 6–2
2019	Jérémy Chardy Fabrice Martin	Luke Bambridge Jonny O'Mara	7–5, 7–6
2020	Not held due to the COVID-19 pandemic.
2021	Hugo Nys Tim Pütz	Luke Bambridge Dominic Inglot	7–5, 3–6, [10–3]
2022	Nuno Borges Francisco Cabral	Máximo González André Göransson	6–2, 6–3
2023	Sander Gillé Joran Vliegen	Nikola Ćaćić Miomir Kecmanović	6–3, 6–4
2024	Gonzalo Escobar Aleksandr Nedovyesov	Sadio Doumbia Fabien Reboul	7–5, 6–2

• Portugal Open (1990–2014)

• Official website
• ATP tournament profile

38°42′29″N 9°15′9″W / 38.70806°N 9.25250°W / 38.70806; -9.25250