CARDIFF, Wales (AP) — Wales' second string proved too strong to Tonga as first-half tries by centers Owen Williams and Ashley Beck set up a scrappy 17-7 win for the Six Nations champions at Millennium Stadium on Friday.

Wales coach Warren Gatland rested the majority of his first-choice players ahead of next week's match against Australia and their replacements lacked the fluency to take full advantage of their dominance of possession in front of 45,000 spectators in Cardiff.

It was still relatively comfortable for the Welsh, though, with Williams taking Leigh Halfpenny's pass and weaving through two tackles to score in the 15th minute and Beck finishing expertly in the left corner in the 24th after George North had made a hole in the Tongan defense.

Halfpenny converted both tries and added a penalty, with Viliami Helu's 33rd-minute converted try being Tonga's only reply prior to a scoreless, error-ridden second half in which the Welsh botched a number of try-scoring opportunities.

"It was pretty ugly out there," Wales lock Luke Charteris said. "We knew going into the match how good a side Tonga were and we were not clinical enough. A team dogged like this will keep putting us under pressure but we won the game."

The result maintained Wales' perfect record against Tonga, extending the winning streak to seven, and built on last weekend's 40-6 victory over Argentina.

Arguably only three starters — Halfpenny, winger George North and possibly lock Ian Evans — would get in Gatland's best side, so it gave the coach an opportunity to test out his fringe players and they began well against a Tonga side that has now lost four games in a row.

Midfield has been a problem area for Gatland as injuries have robbed him of Jamie Roberts, Jonathan Davies and Scott Williams, so Owen Williams and Beck were looking to stake claims for a starting berth against Australia.

Both ended up scoring tries, with Williams' the pick of them as Wales attacked from deep inside its own half before the move ended with Williams smashing through two challenges during a 40-metre charge for his first test try.

After Beck dotted down, the Welsh looked set to run up a big score but they didn't add another point after the 25th minute.

Charteris knocked on with line at his reach in the 62nd and North had a try scrubbed off late on for obstruction.

However, having lost to Samoa last November and only drawn with Fiji in 2010, Wales will be happy to take any win against a Pacific Island nation, especially with most of its best players missing.