Okada was only the second player in history to record a pinch-hit grand slam in 2010, he became the home run king（One of the title of NPB), after Nakanishi Futoshi (Nishitetsu Baseball Club) in 1955.

In the summer, he was called up to the Japanese national baseball team for the Beijing Pre-Olympic Games, and contributed to Japan's victory as a key player.

On September 8th against Lotte, he hit a double off Shunsuke Watanabe and ran to second base, suffering a torn muscle and being diagnosed with a six-week recovery period.

However, eight days later, on September 16th, in a game against Seibu, he came in as a pinch hitter in the bottom of the eighth inning with the score tied and the bases loaded with two outs, and recorded his first grand slam as a professional.

He was also the second player in history to record a pinch-hit grand slam in the same year he became the home-run king, after Futoshi Nakanishi (Nishitetsu) in 1955.

Okada was batting fifth in the first half of the season, but after the game against Lotte on July 3rd, he was settled in the fourth position and showed signs of recovery, recording a team-leading 20 home runs and 76 RBIs.

He was appointed in six different batting orders depending on the team's circumstances, including being used as the leadoff hitter for the first time since turning pro in the game against Nippon Ham on August 5th.

Okada participated in the Puerto Rican winter league as a member of the Atenienses de Manatí (baseball) in 2019.

He played in 115 games, with a batting average of .241, 17 homers, and 63 RBIs, and the team won its first league championship since turning pro.