Allen found some room to move and built up some momentum running down the right win when it all came to a bone crunching halt. Their defense was generally sound, though winger Cooper Vuna and scrumhalf Sonatane Takulua made risky breaks for Tonga in the second half.
Wales' Cory Allen will be feeling the effects of this tackle from Halaifonua for a while.
Wales wing Alex Cuthbert has been ruled out of Friday's Test against Samoa with a shoulder injury.
In the second half, as steady drizzle made handling hard, Takulua closed the gap with his second penalty before Davies added three more for Wales.
In some ways it was job done, especially as the conditions were tricky in the second half, but it was an underwhelming first part of a double-header.More news: WRAPUP 1-Tennis-Highlights of French Open 10th day
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The game was marred with penalties and affected by rain.
From there it became an enterprising but error-ridden spectacle as Wales produced an attacking game but without the necessary finishing touches to put away the Pacific islanders.
But when they drew in the defence they showed no inclination to make the most of the space that opened up out wide.
"I'm still waiting for the call", said a grinning Roberts, a veteran of the 2009 and 2013 tours.
"It was physical, it was a tough battle".
Davies added a penalty, but had two other attempts hit the post, while Tongan scrumhalf Takulua kept the scoreline close with a 23rd-minute penalty.
McBryde's side dominated but failed to convert their superiority into points, and a second successful penalty from scrum-half Sonatone Takulua four minutes after the restart reduced the lead to 8-6. Referee Nick Brian could not see the grounding but awarded a penalty try for the Tongan collapse.