[4] Obasi made his Lyn debut, in the opening game of the season, where he played 66 minutes, in a 1–1 draw against Fredrikstad.

[5] However, Obasi struggled to regain a place in the first team and it wasn't until on 25 September 2005 when he scored his first Lyn goal, in a 1–0 win over Brann.

[14] Several days after he trained with Premier League side Portsmouth, Obasi signed a contract with Lyn, keeping him until 2008.

Throughout his Lyn career, Obasi was linked with moves to European clubs, such as Wigan Athletic,[17] Manchester United, Chelsea,[18] Arsenal[19] and Barcelona.

In a match against Paderborn on 9 March 2008, which saw Hoffenheim win 1–0, Obasi was sent-off in the 54th minute when he was involved in an incident with opposition midfielder Erwin Koen.

[28] In the end, the DFB's control committee decided against taking action against Koen, citing lack of evidence and Obasi served a three match suspension.

[29] Following his return from suspension, Obasi scored four more goals later in the season and helped the club reach promotion to Bundesliga for the first time.

[30] Obasi finished his first season at the club, making thirty appearances and scoring twelve times in all competitions.

[46] It wasn't until on 17 October 2010, when Obasi returned to the first team, coming on as a late substitute, in a 3–2 win over Borussia Mönchengladbach.

[48] After months on the sideline, Obasi returned to the first team in the last game of the season, as a late substitute, in a 3–1 loss against Wolfsburg.

[50] In a match against Stuttgart, which saw them lose 2–0 on 18 October 2011, Obasi was substituted in the second half and when he left the pitch, he refused to shake Holger Stanislawski's hand and was fined as a result.

[51] Seven days later, on 25 October 2011, Obasi scored his first goal of the season, in the second round of DFB-Pokal, in a 2–1 win over Köln.

[52] Obasi continued to remain in the first team for the club until he was dropped from the squad ahead of a match against Hamburg for disobeying orders and a week later when he was late for training.

[64] After returning to training, Obasi then made his first appearance since joining them on a permanent basis in a 2–2 draw against Fortuna Düsseldorf on 28 September 2012.

[78] At the end of the 2014–15 season, Obasi was released by the club after his contract expired and had made ten appearances and one goal in all competitions.

[88] At the end of the season, Obasi moved abroad again when he was recruited by China League One Shenzhen on 4 February 2017, signing a one-year contract and joining manager Sven-Göran Eriksson.

[95] On 21 January 2019 it was announced that Obasi had signed a one-year deal with AIK, his third spell at the Stockholm club.

[96] Obasi was part of the Nigeria national under-20 football team that finished runners-up at the 2005 FIFA World Youth Championship.

[97][98] After the end of the FIFA World Youth Championship, Obasi was called up by the senior national team for the first time on 17 August 2005, in a 1–0 defeat against Libya.

[109] On matchday three, Obasi set up a goal for Yakubu to score an equaliser, in a 2–2 draw against South Korea, but this was not enough for his side to progress out of the group stages.

[111] Since 2011, Obasi hasn't played for the national team, due to injury and being out of form and because he was not released by the club although he was called up on more than one occasion.