Tony Mowbray's side went into the clash at Fratton Park on the back of a confidence-boosting win at Derby and backed that up with a thoroughly-deserved point.
Portsmouth were left frustrated as they wasted a string of chances to beat Smith.
Despite surrendering a six-match winning run against Bristol City on Tuesday, Portsmouth named an unchanged side as they looked to get back on track.
Middlesbrough also kept faith with their starting XI from midweek, but it was Pompey who started the better of the pair and dominated the early exchanges.
David Nugent fashioned the first chance, but his header could only find the hands of Smith.
It was a warning of things to come for Boro as Portsmouth kept the pressure on.
Joel Ward could have tested Smith but his headed effort lacked the power and direction to cause any alarm.
They did come within a whisker after 20 minutes though as another header from Hermann Hreidarsson rattled the bar as he latched onto David Cotterill's free-kick.
Dave Kitson was next to try his luck but brave defending from Rhys Williams' ensured his goal remained in tact.
And after half an hour Mowbray's men made their first foray forward as Jamie Ashdown parried Barry Robson's shot to safety.
That gave the away side an injection of much-needed belief and they worked Ashdown again as Nicky Bailey had a driven shot turned wide.
Middlesbrough began the second period stronger and Scott McDonald forced another save from Ashdown.
Pompey's influence on the game was waning and it was Middlesbrough looking more likely to take home another vital three points.
Steve Cotterill threw on Liam Lawrence and Kanu in search of a breakthrough but they lacked the fluency that had helped them to mount a surge up the table.
Lawrence found room from 20 yards to test Smith but the shot proved to be little more than handling practice.
Smith did do well to keep Pompey at bay as the game reached its final stages, punching away a Nugent header as it threatened to find a way through a crowded area.
But Marvin Emnes - on for the injured Leroy Lita - nearly snatched victory for the visitors as his drive from the left side of penalty area brought another crucial save from Ashdown.