Gérard Houllier gave the right-back his debut when Southampton visited Anfield for a League Cup third round match at the start of November 2002. However, the promising defender had to wait another year for his League debut having featured for Hull in the Third Division in the closing months of the 2002/03 season. In October 2003 he was shot in the buttocks by a small calibre pistol in downtown Liverpool and his car was torched a couple of weeks later near his home. Thankfully he recovered to make five first-team appearances in December 2003 while Steve Finnan was absent through injury. Phil Thompson, Liverpool's assistant manager, was pleased with his contribution: "It's always good for the crowd when a young local lad comes out of the blue, or should that be the red! He's a shy and unassuming lad who gets the job done. He's got great pace and is very composed." Surprisingly, Otsemobor was loaned out to Bolton in February 2004 for the rest of the season but after only appearance in two months Otsemobor cut his stay short even though it meant he was not eligible for Liverpool's first team for the rest of the campaign.
As Rafa Benítez took over he sent Otsemobor on loan to Crewe Alexandra in the Championship for the first half of the 2004/05 season where he made 15 appearances. Despite Crewe's interest Otsemobor wanted to make a final attempt at making a career at Liverpool but it was soon apparent he was not in Benítez' plans. Once his Liverpool contract expired he joined League One Rotherham in the summer, and was on the move again only six months later to Crewe who had been relegated to League One. Otsemobor's contract at Gresty Road expired in June 2007 and he signed a three-year deal with Norwich City in the Championship. He was a regular for a couple of seasons at the Canaries but halfway through 2009/10, after Norwich had been relegated, Otsemobor left East Anglia to sign for another League One club, Southampton. While Norwich took the express route to the Premiership Otsemobor was on the move, this time to Sheffield Wednesday, who had just been relegated to League One. He struggled to earn a regular place, with injuries proving a hindrance, and was released at the end of the 2011/12 season. He subsequently signed a one-year contract with Milton Keynes Dons in League One. Otsemobor soon acquired hero status when he back-heeled the injury-time winner in MK Dons' grudge-match against AFC Wimbledon in the second round of the FA Cup.
The defender, who passed his 30th birthday during the season, played in thirty-five League One matches for Milton Keynes Dons in 2012/13 but his club finished the season in eighth place just outside the play-off places. A third of the way through the 2013/14 season Otsemobor agreed a one-month loan deal with another League One club, Tranmere Rovers. He made 11 appearances in League One during the 2013/14 season (9 for Milton Keynes and 2 for Tranmere) but had to be substituted because of injury only five minutes into his Rovers debut. He also played for Milton Keynes in the League Cup against Northampton Town (Round One) and eventual finalists Sunderland (Round Two). He returned to Milton Keynes from Tranmere and left the Dons by mutual consent on 8 January 2014, making him a free agent as his thirty-first birthday loomed on the horizon. He had a trial with Doncaster Rovers in the summer of 2014 which came to nothing and retired from the game to concentrate on property development.