Namibia's Chrysander Botha failed to kick the ball out and Samoan halfback Kahn Fotuali'i caught it 40m inside Namibia's half and beat a weak tackle from Botha to run all the way to the right hand corner to score, with Tusi Pisi converting the goal.
Namibia were stunned by the Samoan start and struggled to get any quality ball for the first 10 minutes of the match despite looking strong at scrum time.
The African side had one promising chance after 12 minutes when Eugene Jantjies found some space at the lineout 30m from Samoa's try line but the ball was knocked on 5m out and Samoa were able to clear.
Danger signs for Namibia came when Samoa took a quick lineout inside their own half and ran it through their backline for Tuilagi to have some space on the outside, but some brave defence by Danie Dames managed to drive the big winger in to touch.
It was in vain though, because Namibia turned the ball over at the lineout and Samoa ran it to the right then back to the left for Tuilagi to have space again and he scored from a 30m run and Pisi converted to put Samoa 17-0 up 15 minutes into the half.
Samoa kept Namibia under the pump from the kick off and at the 20-minute mark Namibia found themselves penalised at the scrum and Pisi kicked another penalty, this time 38m out from the posts.
Samoa played smart rugby using a tail wind to find field position and put Namibia under pressure but when the Pacific Islanders were 20 points up and 25 minutes had elapsed Pisi was taken from the field with what appeared to be a hamstring injury.
Loose forward Taiasina Tu'ifua also left the paddock with a rib cage injury shortly after.
The injuries seemed to upset Samoa's rhythm for a few minutes until Tuilagi got the ball and ran 18m, dragging three defenders with him, to score his second try, however fullback Paul Williams was unable to convert.
Samoa went a man down when Williams was sin-binned for a shoulder charge on Theuns Kotze just before the break.
With the wind at their backs, Namibia needed to score first after the break and led by captain Jacques Burger they put the pressure on Samoa but his team kept turning the ball over at crucial times.
The first points of the second half came in the 51st minute after Namibia were penalised in front of the posts for an illegal bind in the scrum, Williams who had only just returned from the sin bin slotted it over for three points.
Tulagi got his hat-trick and Samoa's bonus point try in the 55th minute when Namibia failed to find touch and Samoa simply drew and passed and found the big winger who scored under the posts.
Williams scored Samoa's fifth try after a 30m break from openside flanker Maurie Fa'asavalu, although Namibia's spirits were lifted in the 60th minute after a brilliant turnover by Buger it was passed out to Lllewellyn Winkler, who chipped through, re-gathered and passed to Danie Van Wyk who ran 30m to score.
Namibia's chances were made even more difficult when loose forward Rohan Kitshoff was sin-binned for a professional foul.
This fired up the Samoan forwards who opted for three scrums in a row, which resulted in a penalty try.
To Namibia's credit they never gave up thanks to their hard-working captain and centre Van Wyk who looked dangerous whenever he got his hands on the ball.
Their efforts were rewarded in the dying minute when Theuns Kotze broke Samoa's line stretching out and scoring under the posts.
Samoa 49 (Alesana Tuilagi 3, Kahn Fotuali'i, Paul Williams, penalty tries; Tusi Pisi 2 conversions, 2 penalties, Williams 3 conversions, penalty) def. Namibia 12 (Danie Van Wyk, Theuns Kotze tries; Kotze conversion). HT: 25-0.
