He played the full 90 minutes of the goalless draw with Atlético Paranaense at the Arena da Baixada, but he and Juninho had their attempts saved by Vinícius in the penalty shootout, eliminating their team.

On 23 February 2011, as an 80th-minute substitute for Leandro Damião, he scored his first goal for the club to conclude a 4–0 home win over Jaguares de Chiapas at the start of Inter's defence of the Copa Libertadores.

[27] Following his good performances, Oscar became a regular starter in Roberto Di Matteo's creative midfield triumvirate with Juan Mata and Eden Hazard.

Benítez praised Oscar's attitude after dropping him for the FIFA Club World Cup Final against Corinthians and believed there was no rift between himself and the player.

[31] On 14 February 2013, less than a minute after coming off the bench to replace Mata, Oscar exchanged passes with Hazard before finishing past Tomáš Vaclík, breaking the deadlock and handing Chelsea a 1–0 away victory over Sparta Praha in the first leg of their Europa League Round of 32 clash.

[32] On 15 May, Oscar played the full ninety minutes as Chelsea defeated Benfica 2–1 in the Europa League final in Amsterdam, securing his first piece of silverware with the London club.

[36] On 1 January 2014 Oscar put in a match-winning performance against Southampton at St Mary's Stadium, scoring one and assisting two as Chelsea won the match 0–3.

[37] Oscar scored fourth and fifth goals in Chelsea's 6–0 victory over Arsenal on 23 March, which was Arsène Wenger's 1000th match in charge of the club.

[41] On 26 April, he was hospitalised after suffering a head injury following a collision with opposing goalkeeper David Ospina in a 0–0 away draw against Arsenal in the Premier League;[42] he was released the following day.

[43] Oscar scored Chelsea's first goal of the next season in an eventual 2–2 home draw with Swansea, being substituted early in the second half after the dismissal of goalkeeper Thibaut Courtois.

[45] He, Diego Costa and Cesc Fàbregas were abused by supporters who believed that the trio's slump in form had cost the job of popular manager José Mourinho; in the first game since his dismissal, on 26 December, Oscar slipped and missed a spot kick in a 2–2 home draw against Watford.

[46] The following 31 January, Oscar scored a first-half hat-trick in a 5–1 win at Milton Keynes Dons in the fourth round of the FA Cup.

[55] Furthermore, he added that after completing his contract with Shanghai SIPG, he was interested in returning to Europe as he remained motivated to play football at a high level.

[56] Oscar made his official debut on 7 February 2017 and scored the first goal of a 3–0 win over Thai club Sukhothai in the 2017 AFC Champions League qualifying play-off.

[57] On 11 April 2017, Oscar missed two penalty kicks as his team lost 1–0 in an AFC Champions League match against Urawa Red Diamonds.

[5] This performance was immediately compared to the 1966 hat trick by Geoff Hurst as only the second time a single player scored three goals in a World Cup final match.

[76] Oscar starred in Brazil's 3–2 victory over Egypt in the opening game, providing the assists for goals by Rafael and Leandro Damião.

[77][78] In Brazil's next game, a 3–1 victory over Belarus, Oscar netted the Seleção's third goal in injury time, after being played through by Neymar, to send the Brazilians into the quarter-finals.

Oscar provided two assists, one to Rômulo and another for Leandro Damião, as the Seleção defeated South Korea 3–0 in the semi-finals at Old Trafford on 7 August.

[81] Due to injuries to the attacking midfielder Ganso, he saw his national team opportunities increase and was even preferred over more experienced playmakers on a number of occasions.

[83][84] On 25 March 2013 Oscar played against Russia at Stamford Bridge with fellow Chelsea teammates David Luiz and Ramires.

Oscar played and started in all of Brazil's games in the 2013 FIFA Confederations Cup as they beat Spain 3–0 in the final to claim the trophy.

[85] In the opening match of the 2014 FIFA World Cup, on 12 June against Croatia in São Paulo, Oscar scored in injury time with a toe-poke from outside the box for the last goal in a 3–1 win.

[91] A quick, agile, and technically gifted player, with superb dribbling skills and an excellent first touch, Oscar is very fluid and creative in his runs.

As an offensive playmaker, Oscar has great vision and is able to deliver precise short passes to his teammates, which enables him to play "killer balls".

His cunning runs, as well as his skills, range of passing and finishing ability, make him a threat inside or near the opposing penalty area, and allow him to score goals in addition to creating goalscoring opportunities.

Known for his vision, ability to pick out teammates in tight positions, and carve out chances in difficult situations, Oscar often acted as the catalyst in Chelsea's attacks during his time with the club, and was widely praised for his role in the team's Europa League success in 2013.

[94][99][100][101] Despite his talent, however, he has accused by certain pundits – such as Nizaar Kinsella of Goal.com – of being inconsistent, and of failing to live up to his potential, in particular during his later Chelsea career, where he struggled to adapt to different systems and retain his place in the team's starting line-up.

[107] He started taking English classes when he moved to London and became neighbors with former teammate Juan Mata and retired midfielder Giorgos Karagounis upon his arrival at the club.